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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0
 /*
  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  *
  *  Swap reorganised 29.12.95, Stephen Tweedie.
  *  kswapd added: 7.1.96  sct
  *  Removed kswapd_ctl limits, and swap out as many pages as needed
  *  to bring the system back to freepages.high: 2.4.97, Rik van Riel.
  *  Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
  *  Multiqueue VM started 5.8.00, Rik van Riel.
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/mm.h>
 #include <linux/sched/mm.h>
 #include <linux/module.h>
 #include <linux/gfp.h>
 #include <linux/kernel_stat.h>
 #include <linux/swap.h>
 #include <linux/pagemap.h>
 #include <linux/init.h>
 #include <linux/highmem.h>
 #include <linux/vmpressure.h>
 #include <linux/vmstat.h>
 #include <linux/file.h>
 #include <linux/writeback.h>
 #include <linux/blkdev.h>
 #include <linux/buffer_head.h>  /* for buffer_heads_over_limit */
 #include <linux/mm_inline.h>
 #include <linux/backing-dev.h>
 #include <linux/rmap.h>
 #include <linux/topology.h>
 #include <linux/cpu.h>
 #include <linux/cpuset.h>
 #include <linux/compaction.h>
 #include <linux/notifier.h>
 #include <linux/rwsem.h>
 #include <linux/delay.h>
 #include <linux/kthread.h>
 #include <linux/freezer.h>
 #include <linux/memcontrol.h>
 #include <linux/migrate.h>
 #include <linux/delayacct.h>
 #include <linux/sysctl.h>
 #include <linux/oom.h>
 #include <linux/pagevec.h>
 #include <linux/prefetch.h>
 #include <linux/printk.h>
 #include <linux/dax.h>
 #include <linux/psi.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
 
 #include <linux/swapops.h>
 #include <linux/balloon_compaction.h>
 #include <linux/sched/sysctl.h>
 
 #include "internal.h"
 #include "swap.h"
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/vmscan.h>
 
 struct scan_control {
     /* How many pages shrink_list() should reclaim */
     unsigned long nr_to_reclaim;
 
     /*
      * Nodemask of nodes allowed by the caller. If NULL, all nodes
      * are scanned.
      */
     nodemask_t  *nodemask;
 
     /*
      * The memory cgroup that hit its limit and as a result is the
      * primary target of this reclaim invocation.
      */
     struct mem_cgroup *target_mem_cgroup;
 
     /*
      * Scan pressure balancing between anon and file LRUs
      */
     unsigned long   anon_cost;
     unsigned long   file_cost;
 
     /* Can active pages be deactivated as part of reclaim? */
 #define DEACTIVATE_ANON 1
 #define DEACTIVATE_FILE 2
     unsigned int may_deactivate:2;
     unsigned int force_deactivate:1;
     unsigned int skipped_deactivate:1;
 
     /* Writepage batching in laptop mode; RECLAIM_WRITE */
     unsigned int may_writepage:1;
 
     /* Can mapped pages be reclaimed? */
     unsigned int may_unmap:1;
 
     /* Can pages be swapped as part of reclaim? */
     unsigned int may_swap:1;
 
     /* Proactive reclaim invoked by userspace through memory.reclaim */
     unsigned int proactive:1;
 
     /*
      * Cgroup memory below memory.low is protected as long as we
      * don't threaten to OOM. If any cgroup is reclaimed at
      * reduced force or passed over entirely due to its memory.low
      * setting (memcg_low_skipped), and nothing is reclaimed as a
      * result, then go back for one more cycle that reclaims the protected
      * memory (memcg_low_reclaim) to avert OOM.
      */
     unsigned int memcg_low_reclaim:1;
     unsigned int memcg_low_skipped:1;
 
     unsigned int hibernation_mode:1;
 
     /* One of the zones is ready for compaction */
     unsigned int compaction_ready:1;
 
     /* There is easily reclaimable cold cache in the current node */
     unsigned int cache_trim_mode:1;
 
     /* The file pages on the current node are dangerously low */
     unsigned int file_is_tiny:1;
 
     /* Always discard instead of demoting to lower tier memory */
     unsigned int no_demotion:1;
 
     /* Allocation order */
     s8 order;
 
     /* Scan (total_size >> priority) pages at once */
     s8 priority;
 
     /* The highest zone to isolate pages for reclaim from */
     s8 reclaim_idx;
 
     /* This context's GFP mask */
     gfp_t gfp_mask;
 
     /* Incremented by the number of inactive pages that were scanned */
     unsigned long nr_scanned;
 
     /* Number of pages freed so far during a call to shrink_zones() */
     unsigned long nr_reclaimed;
 
     struct {
         unsigned int dirty;
         unsigned int unqueued_dirty;
         unsigned int congested;
         unsigned int writeback;
         unsigned int immediate;
         unsigned int file_taken;
         unsigned int taken;
     } nr;
 
     /* for recording the reclaimed slab by now */
     struct reclaim_state reclaim_state;
 };
 
 #ifdef ARCH_HAS_PREFETCHW
 #define prefetchw_prev_lru_folio(_folio, _base, _field)         \
     do {                                \
         if ((_folio)->lru.prev != _base) {          \
             struct folio *prev;             \
                                     \
             prev = lru_to_folio(&(_folio->lru));        \
             prefetchw(&prev->_field);           \
         }                           \
     } while (0)
 #else
 #define prefetchw_prev_lru_folio(_folio, _base, _field) do { } while (0)
 #endif
 
 /*
  * From 0 .. 200.  Higher means more swappy.
  */
 int vm_swappiness = 60;
 
 static void set_task_reclaim_state(struct task_struct *task,
                    struct reclaim_state *rs)
 {
     /* Check for an overwrite */
     WARN_ON_ONCE(rs && task->reclaim_state);
 
     /* Check for the nulling of an already-nulled member */
     WARN_ON_ONCE(!rs && !task->reclaim_state);
 
     task->reclaim_state = rs;
 }
 
 LIST_HEAD(shrinker_list);
 DECLARE_RWSEM(shrinker_rwsem);
 
 #ifdef CONFIG_MEMCG
 static int shrinker_nr_max;
 
 /* The shrinker_info is expanded in a batch of BITS_PER_LONG */
 static inline int shrinker_map_size(int nr_items)
 {
     return (DIV_ROUND_UP(nr_items, BITS_PER_LONG) * sizeof(unsigned long));
 }
 
 static inline int shrinker_defer_size(int nr_items)
 {
     return (round_up(nr_items, BITS_PER_LONG) * sizeof(atomic_long_t));
 }
 
 static struct shrinker_info *shrinker_info_protected(struct mem_cgroup *memcg,
                              int nid)
 {
     return rcu_dereference_protected(memcg->nodeinfo[nid]->shrinker_info,
                      lockdep_is_held(&shrinker_rwsem));
 }
 
 static int expand_one_shrinker_info(struct mem_cgroup *memcg,
                     int map_size, int defer_size,
                     int old_map_size, int old_defer_size)
 {
     struct shrinker_info *new, *old;
     struct mem_cgroup_per_node *pn;
     int nid;
     int size = map_size + defer_size;
 
     for_each_node(nid) {
         pn = memcg->nodeinfo[nid];
         old = shrinker_info_protected(memcg, nid);
         /* Not yet online memcg */
         if (!old)
             return 0;
 
         new = kvmalloc_node(sizeof(*new) + size, GFP_KERNEL, nid);
         if (!new)
             return -ENOMEM;
 
         new->nr_deferred = (atomic_long_t *)(new + 1);
         new->map = (void *)new->nr_deferred + defer_size;
 
         /* map: set all old bits, clear all new bits */
         memset(new->map, (int)0xff, old_map_size);
         memset((void *)new->map + old_map_size, 0, map_size - old_map_size);
         /* nr_deferred: copy old values, clear all new values */
         memcpy(new->nr_deferred, old->nr_deferred, old_defer_size);
         memset((void *)new->nr_deferred + old_defer_size, 0,
                defer_size - old_defer_size);
 
         rcu_assign_pointer(pn->shrinker_info, new);
         kvfree_rcu(old, rcu);
     }
 
     return 0;
 }
 
 void free_shrinker_info(struct mem_cgroup *memcg)
 {
     struct mem_cgroup_per_node *pn;
     struct shrinker_info *info;
     int nid;
 
     for_each_node(nid) {
         pn = memcg->nodeinfo[nid];
         info = rcu_dereference_protected(pn->shrinker_info, true);
         kvfree(info);
         rcu_assign_pointer(pn->shrinker_info, NULL);
     }
 }
 
 int alloc_shrinker_info(struct mem_cgroup *memcg)
 {
     struct shrinker_info *info;
     int nid, size, ret = 0;
     int map_size, defer_size = 0;
 
     down_write(&shrinker_rwsem);
     map_size = shrinker_map_size(shrinker_nr_max);
     defer_size = shrinker_defer_size(shrinker_nr_max);
     size = map_size + defer_size;
     for_each_node(nid) {
         info = kvzalloc_node(sizeof(*info) + size, GFP_KERNEL, nid);
         if (!info) {
             free_shrinker_info(memcg);
             ret = -ENOMEM;
             break;
         }
         info->nr_deferred = (atomic_long_t *)(info + 1);
         info->map = (void *)info->nr_deferred + defer_size;
         rcu_assign_pointer(memcg->nodeinfo[nid]->shrinker_info, info);
     }
     up_write(&shrinker_rwsem);
 
     return ret;
 }
 
 static inline bool need_expand(int nr_max)
 {
     return round_up(nr_max, BITS_PER_LONG) >
            round_up(shrinker_nr_max, BITS_PER_LONG);
 }
 
 static int expand_shrinker_info(int new_id)
 {
     int ret = 0;
     int new_nr_max = new_id + 1;
     int map_size, defer_size = 0;
     int old_map_size, old_defer_size = 0;
     struct mem_cgroup *memcg;
 
     if (!need_expand(new_nr_max))
         goto out;
 
     if (!root_mem_cgroup)
         goto out;
 
     lockdep_assert_held(&shrinker_rwsem);
 
     map_size = shrinker_map_size(new_nr_max);
     defer_size = shrinker_defer_size(new_nr_max);
     old_map_size = shrinker_map_size(shrinker_nr_max);
     old_defer_size = shrinker_defer_size(shrinker_nr_max);
 
     memcg = mem_cgroup_iter(NULL, NULL, NULL);
     do {
         ret = expand_one_shrinker_info(memcg, map_size, defer_size,
                            old_map_size, old_defer_size);
         if (ret) {
             mem_cgroup_iter_break(NULL, memcg);
             goto out;
         }
     } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
 out:
     if (!ret)
         shrinker_nr_max = new_nr_max;
 
     return ret;
 }
 
 void set_shrinker_bit(struct mem_cgroup *memcg, int nid, int shrinker_id)
 {
     if (shrinker_id >= 0 && memcg && !mem_cgroup_is_root(memcg)) {
         struct shrinker_info *info;
 
         rcu_read_lock();
         info = rcu_dereference(memcg->nodeinfo[nid]->shrinker_info);
         /* Pairs with smp mb in shrink_slab() */
         smp_mb__before_atomic();
         set_bit(shrinker_id, info->map);
         rcu_read_unlock();
     }
 }
 
 static DEFINE_IDR(shrinker_idr);
 
 static int prealloc_memcg_shrinker(struct shrinker *shrinker)
 {
     int id, ret = -ENOMEM;
 
     if (mem_cgroup_disabled())
         return -ENOSYS;
 
     down_write(&shrinker_rwsem);
     /* This may call shrinker, so it must use down_read_trylock() */
     id = idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL);
     if (id < 0)
         goto unlock;
 
     if (id >= shrinker_nr_max) {
         if (expand_shrinker_info(id)) {
             idr_remove(&shrinker_idr, id);
             goto unlock;
         }
     }
     shrinker->id = id;
     ret = 0;
 unlock:
     up_write(&shrinker_rwsem);
     return ret;
 }
 
 static void unregister_memcg_shrinker(struct shrinker *shrinker)
 {
     int id = shrinker->id;
 
     BUG_ON(id < 0);
 
     lockdep_assert_held(&shrinker_rwsem);
 
     idr_remove(&shrinker_idr, id);
 }
 
 static long xchg_nr_deferred_memcg(int nid, struct shrinker *shrinker,
                    struct mem_cgroup *memcg)
 {
     struct shrinker_info *info;
 
     info = shrinker_info_protected(memcg, nid);
     return atomic_long_xchg(&info->nr_deferred[shrinker->id], 0);
 }
 
 static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
                   struct mem_cgroup *memcg)
 {
     struct shrinker_info *info;
 
     info = shrinker_info_protected(memcg, nid);
     return atomic_long_add_return(nr, &info->nr_deferred[shrinker->id]);
 }
 
 void reparent_shrinker_deferred(struct mem_cgroup *memcg)
 {
     int i, nid;
     long nr;
     struct mem_cgroup *parent;
     struct shrinker_info *child_info, *parent_info;
 
     parent = parent_mem_cgroup(memcg);
     if (!parent)
         parent = root_mem_cgroup;
 
     /* Prevent from concurrent shrinker_info expand */
     down_read(&shrinker_rwsem);
     for_each_node(nid) {
         child_info = shrinker_info_protected(memcg, nid);
         parent_info = shrinker_info_protected(parent, nid);
         for (i = 0; i < shrinker_nr_max; i++) {
             nr = atomic_long_read(&child_info->nr_deferred[i]);
             atomic_long_add(nr, &parent_info->nr_deferred[i]);
         }
     }
     up_read(&shrinker_rwsem);
 }
 
 static bool cgroup_reclaim(struct scan_control *sc)
 {
     return sc->target_mem_cgroup;
 }
 
 /**
  * writeback_throttling_sane - is the usual dirty throttling mechanism available?
  * @sc: scan_control in question
  *
  * The normal page dirty throttling mechanism in balance_dirty_pages() is
  * completely broken with the legacy memcg and direct stalling in
  * shrink_page_list() is used for throttling instead, which lacks all the
  * niceties such as fairness, adaptive pausing, bandwidth proportional
  * allocation and configurability.
  *
  * This function tests whether the vmscan currently in progress can assume
  * that the normal dirty throttling mechanism is operational.
  */
 static bool writeback_throttling_sane(struct scan_control *sc)
 {
     if (!cgroup_reclaim(sc))
         return true;
 #ifdef CONFIG_CGROUP_WRITEBACK
     if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
         return true;
 #endif
     return false;
 }
 #else
 static int prealloc_memcg_shrinker(struct shrinker *shrinker)
 {
     return -ENOSYS;
 }
 
 static void unregister_memcg_shrinker(struct shrinker *shrinker)
 {
 }
 
 static long xchg_nr_deferred_memcg(int nid, struct shrinker *shrinker,
                    struct mem_cgroup *memcg)
 {
     return 0;
 }
 
 static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrinker,
                   struct mem_cgroup *memcg)
 {
     return 0;
 }
 
 static bool cgroup_reclaim(struct scan_control *sc)
 {
     return false;
 }
 
 static bool writeback_throttling_sane(struct scan_control *sc)
 {
     return true;
 }
 #endif
 
 static long xchg_nr_deferred(struct shrinker *shrinker,
                  struct shrink_control *sc)
 {
     int nid = sc->nid;
 
     if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
         nid = 0;
 
     if (sc->memcg &&
         (shrinker->flags & SHRINKER_MEMCG_AWARE))
         return xchg_nr_deferred_memcg(nid, shrinker,
                           sc->memcg);
 
     return atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
 }
 
 
 static long add_nr_deferred(long nr, struct shrinker *shrinker,
                 struct shrink_control *sc)
 {
     int nid = sc->nid;
 
     if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
         nid = 0;
 
     if (sc->memcg &&
         (shrinker->flags & SHRINKER_MEMCG_AWARE))
         return add_nr_deferred_memcg(nr, nid, shrinker,
                          sc->memcg);
 
     return atomic_long_add_return(nr, &shrinker->nr_deferred[nid]);
 }
 
 static bool can_demote(int nid, struct scan_control *sc)
 {
     if (!numa_demotion_enabled)
         return false;
     if (sc && sc->no_demotion)
         return false;
     if (next_demotion_node(nid) == NUMA_NO_NODE)
         return false;
 
     return true;
 }
 
 static inline bool can_reclaim_anon_pages(struct mem_cgroup *memcg,
                       int nid,
                       struct scan_control *sc)
 {
     if (memcg == NULL) {
         /*
          * For non-memcg reclaim, is there
          * space in any swap device?
          */
         if (get_nr_swap_pages() > 0)
             return true;
     } else {
         /* Is the memcg below its swap limit? */
         if (mem_cgroup_get_nr_swap_pages(memcg) > 0)
             return true;
     }
 
     /*
      * The page can not be swapped.
      *
      * Can it be reclaimed from this node via demotion?
      */
     return can_demote(nid, sc);
 }
 
 /*
  * This misses isolated pages which are not accounted for to save counters.
  * As the data only determines if reclaim or compaction continues, it is
  * not expected that isolated pages will be a dominating factor.
  */
 unsigned long zone_reclaimable_pages(struct zone *zone)
 {
     unsigned long nr;
 
     nr = zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_FILE) +
         zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_FILE);
     if (can_reclaim_anon_pages(NULL, zone_to_nid(zone), NULL))
         nr += zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_ANON) +
             zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_ANON);
 
     return nr;
 }
 
 /**
  * lruvec_lru_size -  Returns the number of pages on the given LRU list.
  * @lruvec: lru vector
  * @lru: lru to use
  * @zone_idx: zones to consider (use MAX_NR_ZONES - 1 for the whole LRU list)
  */
 static unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru,
                      int zone_idx)
 {
     unsigned long size = 0;
     int zid;
 
     for (zid = 0; zid <= zone_idx; zid++) {
         struct zone *zone = &lruvec_pgdat(lruvec)->node_zones[zid];
 
         if (!managed_zone(zone))
             continue;
 
         if (!mem_cgroup_disabled())
             size += mem_cgroup_get_zone_lru_size(lruvec, lru, zid);
         else
             size += zone_page_state(zone, NR_ZONE_LRU_BASE + lru);
     }
     return size;
 }
 
 /*
  * Add a shrinker callback to be called from the vm.
  */
 static int __prealloc_shrinker(struct shrinker *shrinker)
 {
     unsigned int size;
     int err;
 
     if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
         err = prealloc_memcg_shrinker(shrinker);
         if (err != -ENOSYS)
             return err;
 
         shrinker->flags &= ~SHRINKER_MEMCG_AWARE;
     }
 
     size = sizeof(*shrinker->nr_deferred);
     if (shrinker->flags & SHRINKER_NUMA_AWARE)
         size *= nr_node_ids;
 
     shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
     if (!shrinker->nr_deferred)
         return -ENOMEM;
 
     return 0;
 }
 
 #ifdef CONFIG_SHRINKER_DEBUG
 int prealloc_shrinker(struct shrinker *shrinker, const char *fmt, ...)
 {
     va_list ap;
     int err;
 
     va_start(ap, fmt);
     shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, ap);
     va_end(ap);
     if (!shrinker->name)
         return -ENOMEM;
 
     err = __prealloc_shrinker(shrinker);
     if (err) {
         kfree_const(shrinker->name);
         shrinker->name = NULL;
     }
 
     return err;
 }
 #else
 int prealloc_shrinker(struct shrinker *shrinker, const char *fmt, ...)
 {
     return __prealloc_shrinker(shrinker);
 }
 #endif
 
 void free_prealloced_shrinker(struct shrinker *shrinker)
 {
 #ifdef CONFIG_SHRINKER_DEBUG
     kfree_const(shrinker->name);
     shrinker->name = NULL;
 #endif
     if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
         down_write(&shrinker_rwsem);
         unregister_memcg_shrinker(shrinker);
         up_write(&shrinker_rwsem);
         return;
     }
 
     kfree(shrinker->nr_deferred);
     shrinker->nr_deferred = NULL;
 }
 
 void register_shrinker_prepared(struct shrinker *shrinker)
 {
     down_write(&shrinker_rwsem);
     list_add_tail(&shrinker->list, &shrinker_list);
     shrinker->flags |= SHRINKER_REGISTERED;
     shrinker_debugfs_add(shrinker);
     up_write(&shrinker_rwsem);
 }
 
 static int __register_shrinker(struct shrinker *shrinker)
 {
     int err = __prealloc_shrinker(shrinker);
 
     if (err)
         return err;
     register_shrinker_prepared(shrinker);
     return 0;
 }
 
 #ifdef CONFIG_SHRINKER_DEBUG
 int register_shrinker(struct shrinker *shrinker, const char *fmt, ...)
 {
     va_list ap;
     int err;
 
     va_start(ap, fmt);
     shrinker->name = kvasprintf_const(GFP_KERNEL, fmt, ap);
     va_end(ap);
     if (!shrinker->name)
         return -ENOMEM;
 
     err = __register_shrinker(shrinker);
     if (err) {
         kfree_const(shrinker->name);
         shrinker->name = NULL;
     }
     return err;
 }
 #else
 int register_shrinker(struct shrinker *shrinker, const char *fmt, ...)
 {
     return __register_shrinker(shrinker);
 }
 #endif
 EXPORT_SYMBOL(register_shrinker);
 
 /*
  * Remove one
  */
 void unregister_shrinker(struct shrinker *shrinker)
 {
     if (!(shrinker->flags & SHRINKER_REGISTERED))
         return;
 
     down_write(&shrinker_rwsem);
     list_del(&shrinker->list);
     shrinker->flags &= ~SHRINKER_REGISTERED;
     if (shrinker->flags & SHRINKER_MEMCG_AWARE)
         unregister_memcg_shrinker(shrinker);
     shrinker_debugfs_remove(shrinker);
     up_write(&shrinker_rwsem);
 
     kfree(shrinker->nr_deferred);
     shrinker->nr_deferred = NULL;
 }
 EXPORT_SYMBOL(unregister_shrinker);
 
 /**
  * synchronize_shrinkers - Wait for all running shrinkers to complete.
  *
  * This is equivalent to calling unregister_shrink() and register_shrinker(),
  * but atomically and with less overhead. This is useful to guarantee that all
  * shrinker invocations have seen an update, before freeing memory, similar to
  * rcu.
  */
 void synchronize_shrinkers(void)
 {
     down_write(&shrinker_rwsem);
     up_write(&shrinker_rwsem);
 }
 EXPORT_SYMBOL(synchronize_shrinkers);
 
 #define SHRINK_BATCH 128
 
 static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
                     struct shrinker *shrinker, int priority)
 {
     unsigned long freed = 0;
     unsigned long long delta;
     long total_scan;
     long freeable;
     long nr;
     long new_nr;
     long batch_size = shrinker->batch ? shrinker->batch
                       : SHRINK_BATCH;
     long scanned = 0, next_deferred;
 
     freeable = shrinker->count_objects(shrinker, shrinkctl);
     if (freeable == 0 || freeable == SHRINK_EMPTY)
         return freeable;
 
     /*
      * copy the current shrinker scan count into a local variable
      * and zero it so that other concurrent shrinker invocations
      * don't also do this scanning work.
      */
     nr = xchg_nr_deferred(shrinker, shrinkctl);
 
     if (shrinker->seeks) {
         delta = freeable >> priority;
         delta *= 4;
         do_div(delta, shrinker->seeks);
     } else {
         /*
          * These objects don't require any IO to create. Trim
          * them aggressively under memory pressure to keep
          * them from causing refetches in the IO caches.
          */
         delta = freeable / 2;
     }
 
     total_scan = nr >> priority;
     total_scan += delta;
     total_scan = min(total_scan, (2 * freeable));
 
     trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
                    freeable, delta, total_scan, priority);
 
     /*
      * Normally, we should not scan less than batch_size objects in one
      * pass to avoid too frequent shrinker calls, but if the slab has less
      * than batch_size objects in total and we are really tight on memory,
      * we will try to reclaim all available objects, otherwise we can end
      * up failing allocations although there are plenty of reclaimable
      * objects spread over several slabs with usage less than the
      * batch_size.
      *
      * We detect the "tight on memory" situations by looking at the total
      * number of objects we want to scan (total_scan). If it is greater
      * than the total number of objects on slab (freeable), we must be
      * scanning at high prio and therefore should try to reclaim as much as
      * possible.
      */
     while (total_scan >= batch_size ||
            total_scan >= freeable) {
         unsigned long ret;
         unsigned long nr_to_scan = min(batch_size, total_scan);
 
         shrinkctl->nr_to_scan = nr_to_scan;
         shrinkctl->nr_scanned = nr_to_scan;
         ret = shrinker->scan_objects(shrinker, shrinkctl);
         if (ret == SHRINK_STOP)
             break;
         freed += ret;
 
         count_vm_events(SLABS_SCANNED, shrinkctl->nr_scanned);
         total_scan -= shrinkctl->nr_scanned;
         scanned += shrinkctl->nr_scanned;
 
         cond_resched();
     }
 
     /*
      * The deferred work is increased by any new work (delta) that wasn't
      * done, decreased by old deferred work that was done now.
      *
      * And it is capped to two times of the freeable items.
      */
     next_deferred = max_t(long, (nr + delta - scanned), 0);
     next_deferred = min(next_deferred, (2 * freeable));
 
     /*
      * move the unused scan count back into the shrinker in a
      * manner that handles concurrent updates.
      */
     new_nr = add_nr_deferred(next_deferred, shrinker, shrinkctl);
 
     trace_mm_shrink_slab_end(shrinker, shrinkctl->nid, freed, nr, new_nr, total_scan);
     return freed;
 }
 
 #ifdef CONFIG_MEMCG
 static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
             struct mem_cgroup *memcg, int priority)
 {
     struct shrinker_info *info;
     unsigned long ret, freed = 0;
     int i;
 
     if (!mem_cgroup_online(memcg))
         return 0;
 
     if (!down_read_trylock(&shrinker_rwsem))
         return 0;
 
     info = shrinker_info_protected(memcg, nid);
     if (unlikely(!info))
         goto unlock;
 
     for_each_set_bit(i, info->map, shrinker_nr_max) {
         struct shrink_control sc = {
             .gfp_mask = gfp_mask,
             .nid = nid,
             .memcg = memcg,
         };
         struct shrinker *shrinker;
 
         shrinker = idr_find(&shrinker_idr, i);
         if (unlikely(!shrinker || !(shrinker->flags & SHRINKER_REGISTERED))) {
             if (!shrinker)
                 clear_bit(i, info->map);
             continue;
         }
 
         /* Call non-slab shrinkers even though kmem is disabled */
         if (!memcg_kmem_enabled() &&
             !(shrinker->flags & SHRINKER_NONSLAB))
             continue;
 
         ret = do_shrink_slab(&sc, shrinker, priority);
         if (ret == SHRINK_EMPTY) {
             clear_bit(i, info->map);
             /*
              * After the shrinker reported that it had no objects to
              * free, but before we cleared the corresponding bit in
              * the memcg shrinker map, a new object might have been
              * added. To make sure, we have the bit set in this
              * case, we invoke the shrinker one more time and reset
              * the bit if it reports that it is not empty anymore.
              * The memory barrier here pairs with the barrier in
              * set_shrinker_bit():
              *
              * list_lru_add()     shrink_slab_memcg()
              *   list_add_tail()    clear_bit()
              *   <MB>               <MB>
              *   set_bit()          do_shrink_slab()
              */
             smp_mb__after_atomic();
             ret = do_shrink_slab(&sc, shrinker, priority);
             if (ret == SHRINK_EMPTY)
                 ret = 0;
             else
                 set_shrinker_bit(memcg, nid, i);
         }
         freed += ret;
 
         if (rwsem_is_contended(&shrinker_rwsem)) {
             freed = freed ? : 1;
             break;
         }
     }
 unlock:
     up_read(&shrinker_rwsem);
     return freed;
 }
 #else /* CONFIG_MEMCG */
 static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid,
             struct mem_cgroup *memcg, int priority)
 {
     return 0;
 }
 #endif /* CONFIG_MEMCG */
 
 /**
  * shrink_slab - shrink slab caches
  * @gfp_mask: allocation context
  * @nid: node whose slab caches to target
  * @memcg: memory cgroup whose slab caches to target
  * @priority: the reclaim priority
  *
  * Call the shrink functions to age shrinkable caches.
  *
  * @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set,
  * unaware shrinkers will receive a node id of 0 instead.
  *
  * @memcg specifies the memory cgroup to target. Unaware shrinkers
  * are called only if it is the root cgroup.
  *
  * @priority is sc->priority, we take the number of objects and >> by priority
  * in order to get the scan target.
  *
  * Returns the number of reclaimed slab objects.
  */
 static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
                  struct mem_cgroup *memcg,
                  int priority)
 {
     unsigned long ret, freed = 0;
     struct shrinker *shrinker;
 
     /*
      * The root memcg might be allocated even though memcg is disabled
      * via "cgroup_disable=memory" boot parameter.  This could make
      * mem_cgroup_is_root() return false, then just run memcg slab
      * shrink, but skip global shrink.  This may result in premature
      * oom.
      */
     if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg))
         return shrink_slab_memcg(gfp_mask, nid, memcg, priority);
 
     if (!down_read_trylock(&shrinker_rwsem))
         goto out;
 
     list_for_each_entry(shrinker, &shrinker_list, list) {
         struct shrink_control sc = {
             .gfp_mask = gfp_mask,
             .nid = nid,
             .memcg = memcg,
         };
 
         ret = do_shrink_slab(&sc, shrinker, priority);
         if (ret == SHRINK_EMPTY)
             ret = 0;
         freed += ret;
         /*
          * Bail out if someone want to register a new shrinker to
          * prevent the registration from being stalled for long periods
          * by parallel ongoing shrinking.
          */
         if (rwsem_is_contended(&shrinker_rwsem)) {
             freed = freed ? : 1;
             break;
         }
     }
 
     up_read(&shrinker_rwsem);
 out:
     cond_resched();
     return freed;
 }
 
 static void drop_slab_node(int nid)
 {
     unsigned long freed;
     int shift = 0;
 
     do {
         struct mem_cgroup *memcg = NULL;
 
         if (fatal_signal_pending(current))
             return;
 
         freed = 0;
         memcg = mem_cgroup_iter(NULL, NULL, NULL);
         do {
             freed += shrink_slab(GFP_KERNEL, nid, memcg, 0);
         } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
     } while ((freed >> shift++) > 1);
 }
 
 void drop_slab(void)
 {
     int nid;
 
     for_each_online_node(nid)
         drop_slab_node(nid);
 }
 
 static inline int is_page_cache_freeable(struct folio *folio)
 {
     /*
      * A freeable page cache page is referenced only by the caller
      * that isolated the page, the page cache and optional buffer
      * heads at page->private.
      */
     return folio_ref_count(folio) - folio_test_private(folio) ==
         1 + folio_nr_pages(folio);
 }
 
 /*
  * We detected a synchronous write error writing a folio out.  Probably
  * -ENOSPC.  We need to propagate that into the address_space for a subsequent
  * fsync(), msync() or close().
  *
  * The tricky part is that after writepage we cannot touch the mapping: nothing
  * prevents it from being freed up.  But we have a ref on the folio and once
  * that folio is locked, the mapping is pinned.
  *
  * We're allowed to run sleeping folio_lock() here because we know the caller has
  * __GFP_FS.
  */
 static void handle_write_error(struct address_space *mapping,
                 struct folio *folio, int error)
 {
     folio_lock(folio);
     if (folio_mapping(folio) == mapping)
         mapping_set_error(mapping, error);
     folio_unlock(folio);
 }
 
 static bool skip_throttle_noprogress(pg_data_t *pgdat)
 {
     int reclaimable = 0, write_pending = 0;
     int i;
 
     /*
      * If kswapd is disabled, reschedule if necessary but do not
      * throttle as the system is likely near OOM.
      */
     if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
         return true;
 
     /*
      * If there are a lot of dirty/writeback pages then do not
      * throttle as throttling will occur when the pages cycle
      * towards the end of the LRU if still under writeback.
      */
     for (i = 0; i < MAX_NR_ZONES; i++) {
         struct zone *zone = pgdat->node_zones + i;
 
         if (!managed_zone(zone))
             continue;
 
         reclaimable += zone_reclaimable_pages(zone);
         write_pending += zone_page_state_snapshot(zone,
                           NR_ZONE_WRITE_PENDING);
     }
     if (2 * write_pending <= reclaimable)
         return true;
 
     return false;
 }
 
 void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason)
 {
     wait_queue_head_t *wqh = &pgdat->reclaim_wait[reason];
     long timeout, ret;
     DEFINE_WAIT(wait);
 
     /*
      * Do not throttle IO workers, kthreads other than kswapd or
      * workqueues. They may be required for reclaim to make
      * forward progress (e.g. journalling workqueues or kthreads).
      */
     if (!current_is_kswapd() &&
         current->flags & (PF_IO_WORKER|PF_KTHREAD)) {
         cond_resched();
         return;
     }
 
     /*
      * These figures are pulled out of thin air.
      * VMSCAN_THROTTLE_ISOLATED is a transient condition based on too many
      * parallel reclaimers which is a short-lived event so the timeout is
      * short. Failing to make progress or waiting on writeback are
      * potentially long-lived events so use a longer timeout. This is shaky
      * logic as a failure to make progress could be due to anything from
      * writeback to a slow device to excessive references pages at the tail
      * of the inactive LRU.
      */
     switch(reason) {
     case VMSCAN_THROTTLE_WRITEBACK:
         timeout = HZ/10;
 
         if (atomic_inc_return(&pgdat->nr_writeback_throttled) == 1) {
             WRITE_ONCE(pgdat->nr_reclaim_start,
                 node_page_state(pgdat, NR_THROTTLED_WRITTEN));
         }
 
         break;
     case VMSCAN_THROTTLE_CONGESTED:
         fallthrough;
     case VMSCAN_THROTTLE_NOPROGRESS:
         if (skip_throttle_noprogress(pgdat)) {
             cond_resched();
             return;
         }
 
         timeout = 1;
 
         break;
     case VMSCAN_THROTTLE_ISOLATED:
         timeout = HZ/50;
         break;
     default:
         WARN_ON_ONCE(1);
         timeout = HZ;
         break;
     }
 
     prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
     ret = schedule_timeout(timeout);
     finish_wait(wqh, &wait);
 
     if (reason == VMSCAN_THROTTLE_WRITEBACK)
         atomic_dec(&pgdat->nr_writeback_throttled);
 
     trace_mm_vmscan_throttled(pgdat->node_id, jiffies_to_usecs(timeout),
                 jiffies_to_usecs(timeout - ret),
                 reason);
 }
 
 /*
  * Account for pages written if tasks are throttled waiting on dirty
  * pages to clean. If enough pages have been cleaned since throttling
  * started then wakeup the throttled tasks.
  */
 void __acct_reclaim_writeback(pg_data_t *pgdat, struct folio *folio,
                             int nr_throttled)
 {
     unsigned long nr_written;
 
     node_stat_add_folio(folio, NR_THROTTLED_WRITTEN);
 
     /*
      * This is an inaccurate read as the per-cpu deltas may not
      * be synchronised. However, given that the system is
      * writeback throttled, it is not worth taking the penalty
      * of getting an accurate count. At worst, the throttle
      * timeout guarantees forward progress.
      */
     nr_written = node_page_state(pgdat, NR_THROTTLED_WRITTEN) -
         READ_ONCE(pgdat->nr_reclaim_start);
 
     if (nr_written > SWAP_CLUSTER_MAX * nr_throttled)
         wake_up(&pgdat->reclaim_wait[VMSCAN_THROTTLE_WRITEBACK]);
 }
 
 /* possible outcome of pageout() */
 typedef enum {
     /* failed to write page out, page is locked */
     PAGE_KEEP,
     /* move page to the active list, page is locked */
     PAGE_ACTIVATE,
     /* page has been sent to the disk successfully, page is unlocked */
     PAGE_SUCCESS,
     /* page is clean and locked */
     PAGE_CLEAN,
 } pageout_t;
 
 /*
  * pageout is called by shrink_page_list() for each dirty page.
  * Calls ->writepage().
  */
 static pageout_t pageout(struct folio *folio, struct address_space *mapping,
              struct swap_iocb **plug)
 {
     /*
      * If the folio is dirty, only perform writeback if that write
      * will be non-blocking.  To prevent this allocation from being
      * stalled by pagecache activity.  But note that there may be
      * stalls if we need to run get_block().  We could test
      * PagePrivate for that.
      *
      * If this process is currently in __generic_file_write_iter() against
      * this folio's queue, we can perform writeback even if that
      * will block.
      *
      * If the folio is swapcache, write it back even if that would
      * block, for some throttling. This happens by accident, because
      * swap_backing_dev_info is bust: it doesn't reflect the
      * congestion state of the swapdevs.  Easy to fix, if needed.
      */
     if (!is_page_cache_freeable(folio))
         return PAGE_KEEP;
     if (!mapping) {
         /*
          * Some data journaling orphaned folios can have
          * folio->mapping == NULL while being dirty with clean buffers.
          */
         if (folio_test_private(folio)) {
             if (try_to_free_buffers(folio)) {
                 folio_clear_dirty(folio);
                 pr_info("%s: orphaned folio\n", __func__);
                 return PAGE_CLEAN;
             }
         }
         return PAGE_KEEP;
     }
     if (mapping->a_ops->writepage == NULL)
         return PAGE_ACTIVATE;
 
     if (folio_clear_dirty_for_io(folio)) {
         int res;
         struct writeback_control wbc = {
             .sync_mode = WB_SYNC_NONE,
             .nr_to_write = SWAP_CLUSTER_MAX,
             .range_start = 0,
             .range_end = LLONG_MAX,
             .for_reclaim = 1,
             .swap_plug = plug,
         };
 
         folio_set_reclaim(folio);
         res = mapping->a_ops->writepage(&folio->page, &wbc);
         if (res < 0)
             handle_write_error(mapping, folio, res);
         if (res == AOP_WRITEPAGE_ACTIVATE) {
             folio_clear_reclaim(folio);
             return PAGE_ACTIVATE;
         }
 
         if (!folio_test_writeback(folio)) {
             /* synchronous write or broken a_ops? */
             folio_clear_reclaim(folio);
         }
         trace_mm_vmscan_write_folio(folio);
         node_stat_add_folio(folio, NR_VMSCAN_WRITE);
         return PAGE_SUCCESS;
     }
 
     return PAGE_CLEAN;
 }
 
 /*
  * Same as remove_mapping, but if the page is removed from the mapping, it
  * gets returned with a refcount of 0.
  */
 static int __remove_mapping(struct address_space *mapping, struct folio *folio,
                 bool reclaimed, struct mem_cgroup *target_memcg)
 {
     int refcount;
     void *shadow = NULL;
 
     BUG_ON(!folio_test_locked(folio));
     BUG_ON(mapping != folio_mapping(folio));
 
     if (!folio_test_swapcache(folio))
         spin_lock(&mapping->host->i_lock);
     xa_lock_irq(&mapping->i_pages);
     /*
      * The non racy check for a busy page.
      *
      * Must be careful with the order of the tests. When someone has
      * a ref to the page, it may be possible that they dirty it then
      * drop the reference. So if PageDirty is tested before page_count
      * here, then the following race may occur:
      *
      * get_user_pages(&page);
      * [user mapping goes away]
      * write_to(page);
      *              !PageDirty(page)    [good]
      * SetPageDirty(page);
      * put_page(page);
      *              !page_count(page)   [good, discard it]
      *
      * [oops, our write_to data is lost]
      *
      * Reversing the order of the tests ensures such a situation cannot
      * escape unnoticed. The smp_rmb is needed to ensure the page->flags
      * load is not satisfied before that of page->_refcount.
      *
      * Note that if SetPageDirty is always performed via set_page_dirty,
      * and thus under the i_pages lock, then this ordering is not required.
      */
     refcount = 1 + folio_nr_pages(folio);
     if (!folio_ref_freeze(folio, refcount))
         goto cannot_free;
     /* note: atomic_cmpxchg in page_ref_freeze provides the smp_rmb */
     if (unlikely(folio_test_dirty(folio))) {
         folio_ref_unfreeze(folio, refcount);
         goto cannot_free;
     }
 
     if (folio_test_swapcache(folio)) {
         swp_entry_t swap = folio_swap_entry(folio);
         mem_cgroup_swapout(folio, swap);
         if (reclaimed && !mapping_exiting(mapping))
             shadow = workingset_eviction(folio, target_memcg);
         __delete_from_swap_cache(folio, swap, shadow);
         xa_unlock_irq(&mapping->i_pages);
         put_swap_page(&folio->page, swap);
     } else {
         void (*free_folio)(struct folio *);
 
         free_folio = mapping->a_ops->free_folio;
         /*
          * Remember a shadow entry for reclaimed file cache in
          * order to detect refaults, thus thrashing, later on.
          *
          * But don't store shadows in an address space that is
          * already exiting.  This is not just an optimization,
          * inode reclaim needs to empty out the radix tree or
          * the nodes are lost.  Don't plant shadows behind its
          * back.
          *
          * We also don't store shadows for DAX mappings because the
          * only page cache pages found in these are zero pages
          * covering holes, and because we don't want to mix DAX
          * exceptional entries and shadow exceptional entries in the
          * same address_space.
          */
         if (reclaimed && folio_is_file_lru(folio) &&
             !mapping_exiting(mapping) && !dax_mapping(mapping))
             shadow = workingset_eviction(folio, target_memcg);
         __filemap_remove_folio(folio, shadow);
         xa_unlock_irq(&mapping->i_pages);
         if (mapping_shrinkable(mapping))
             inode_add_lru(mapping->host);
         spin_unlock(&mapping->host->i_lock);
 
         if (free_folio)
             free_folio(folio);
     }
 
     return 1;
 
 cannot_free:
     xa_unlock_irq(&mapping->i_pages);
     if (!folio_test_swapcache(folio))
         spin_unlock(&mapping->host->i_lock);
     return 0;
 }
 
 /**
  * remove_mapping() - Attempt to remove a folio from its mapping.
  * @mapping: The address space.
  * @folio: The folio to remove.
  *
  * If the folio is dirty, under writeback or if someone else has a ref
  * on it, removal will fail.
  * Return: The number of pages removed from the mapping.  0 if the folio
  * could not be removed.
  * Context: The caller should have a single refcount on the folio and
  * hold its lock.
  */
 long remove_mapping(struct address_space *mapping, struct folio *folio)
 {
     if (__remove_mapping(mapping, folio, false, NULL)) {
         /*
          * Unfreezing the refcount with 1 effectively
          * drops the pagecache ref for us without requiring another
          * atomic operation.
          */
         folio_ref_unfreeze(folio, 1);
         return folio_nr_pages(folio);
     }
     return 0;
 }
 
 /**
  * folio_putback_lru - Put previously isolated folio onto appropriate LRU list.
  * @folio: Folio to be returned to an LRU list.
  *
  * Add previously isolated @folio to appropriate LRU list.
  * The folio may still be unevictable for other reasons.
  *
  * Context: lru_lock must not be held, interrupts must be enabled.
  */
 void folio_putback_lru(struct folio *folio)
 {
     folio_add_lru(folio);
     folio_put(folio);       /* drop ref from isolate */
 }
 
 enum page_references {
     PAGEREF_RECLAIM,
     PAGEREF_RECLAIM_CLEAN,
     PAGEREF_KEEP,
     PAGEREF_ACTIVATE,
 };
 
 static enum page_references folio_check_references(struct folio *folio,
                           struct scan_control *sc)
 {
     int referenced_ptes, referenced_folio;
     unsigned long vm_flags;
 
     referenced_ptes = folio_referenced(folio, 1, sc->target_mem_cgroup,
                        &vm_flags);
     referenced_folio = folio_test_clear_referenced(folio);
 
     /*
      * The supposedly reclaimable folio was found to be in a VM_LOCKED vma.
      * Let the folio, now marked Mlocked, be moved to the unevictable list.
      */
     if (vm_flags & VM_LOCKED)
         return PAGEREF_ACTIVATE;
 
     /* rmap lock contention: rotate */
     if (referenced_ptes == -1)
         return PAGEREF_KEEP;
 
     if (referenced_ptes) {
         /*
          * All mapped folios start out with page table
          * references from the instantiating fault, so we need
          * to look twice if a mapped file/anon folio is used more
          * than once.
          *
          * Mark it and spare it for another trip around the
          * inactive list.  Another page table reference will
          * lead to its activation.
          *
          * Note: the mark is set for activated folios as well
          * so that recently deactivated but used folios are
          * quickly recovered.
          */
         folio_set_referenced(folio);
 
         if (referenced_folio || referenced_ptes > 1)
             return PAGEREF_ACTIVATE;
 
         /*
          * Activate file-backed executable folios after first usage.
          */
         if ((vm_flags & VM_EXEC) && folio_is_file_lru(folio))
             return PAGEREF_ACTIVATE;
 
         return PAGEREF_KEEP;
     }
 
     /* Reclaim if clean, defer dirty folios to writeback */
     if (referenced_folio && folio_is_file_lru(folio))
         return PAGEREF_RECLAIM_CLEAN;
 
     return PAGEREF_RECLAIM;
 }
 
 /* Check if a page is dirty or under writeback */
 static void folio_check_dirty_writeback(struct folio *folio,
                        bool *dirty, bool *writeback)
 {
     struct address_space *mapping;
 
     /*
      * Anonymous pages are not handled by flushers and must be written
      * from reclaim context. Do not stall reclaim based on them.
      * MADV_FREE anonymous pages are put into inactive file list too.
      * They could be mistakenly treated as file lru. So further anon
      * test is needed.
      */
     if (!folio_is_file_lru(folio) ||
         (folio_test_anon(folio) && !folio_test_swapbacked(folio))) {
         *dirty = false;
         *writeback = false;
         return;
     }
 
     /* By default assume that the folio flags are accurate */
     *dirty = folio_test_dirty(folio);
     *writeback = folio_test_writeback(folio);
 
     /* Verify dirty/writeback state if the filesystem supports it */
     if (!folio_test_private(folio))
         return;
 
     mapping = folio_mapping(folio);
     if (mapping && mapping->a_ops->is_dirty_writeback)
         mapping->a_ops->is_dirty_writeback(folio, dirty, writeback);
 }
 
 static struct page *alloc_demote_page(struct page *page, unsigned long node)
 {
     struct migration_target_control mtc = {
         /*
          * Allocate from 'node', or fail quickly and quietly.
          * When this happens, 'page' will likely just be discarded
          * instead of migrated.
          */
         .gfp_mask = (GFP_HIGHUSER_MOVABLE & ~__GFP_RECLAIM) |
                 __GFP_THISNODE  | __GFP_NOWARN |
                 __GFP_NOMEMALLOC | GFP_NOWAIT,
         .nid = node
     };
 
     return alloc_migration_target(page, (unsigned long)&mtc);
 }
 
 /*
  * Take pages on @demote_list and attempt to demote them to
  * another node.  Pages which are not demoted are left on
  * @demote_pages.
  */
 static unsigned int demote_page_list(struct list_head *demote_pages,
                      struct pglist_data *pgdat)
 {
     int target_nid = next_demotion_node(pgdat->node_id);
     unsigned int nr_succeeded;
 
     if (list_empty(demote_pages))
         return 0;
 
     if (target_nid == NUMA_NO_NODE)
         return 0;
 
     /* Demotion ignores all cpuset and mempolicy settings */
     migrate_pages(demote_pages, alloc_demote_page, NULL,
                 target_nid, MIGRATE_ASYNC, MR_DEMOTION,
                 &nr_succeeded);
 
     if (current_is_kswapd())
         __count_vm_events(PGDEMOTE_KSWAPD, nr_succeeded);
     else
         __count_vm_events(PGDEMOTE_DIRECT, nr_succeeded);
 
     return nr_succeeded;
 }
 
 static bool may_enter_fs(struct folio *folio, gfp_t gfp_mask)
 {
     if (gfp_mask & __GFP_FS)
         return true;
     if (!folio_test_swapcache(folio) || !(gfp_mask & __GFP_IO))
         return false;
     /*
      * We can "enter_fs" for swap-cache with only __GFP_IO
      * providing this isn't SWP_FS_OPS.
      * ->flags can be updated non-atomicially (scan_swap_map_slots),
      * but that will never affect SWP_FS_OPS, so the data_race
      * is safe.
      */
     return !data_race(folio_swap_flags(folio) & SWP_FS_OPS);
 }
 
 /*
  * shrink_page_list() returns the number of reclaimed pages
  */
 static unsigned int shrink_page_list(struct list_head *page_list,
                      struct pglist_data *pgdat,
                      struct scan_control *sc,
                      struct reclaim_stat *stat,
                      bool ignore_references)
 {
     LIST_HEAD(ret_pages);
     LIST_HEAD(free_pages);
     LIST_HEAD(demote_pages);
     unsigned int nr_reclaimed = 0;
     unsigned int pgactivate = 0;
     bool do_demote_pass;
     struct swap_iocb *plug = NULL;
 
     memset(stat, 0, sizeof(*stat));
     cond_resched();
     do_demote_pass = can_demote(pgdat->node_id, sc);
 
 retry:
     while (!list_empty(page_list)) {
         struct address_space *mapping;
         struct folio *folio;
         enum page_references references = PAGEREF_RECLAIM;
         bool dirty, writeback;
         unsigned int nr_pages;
 
         cond_resched();
 
         folio = lru_to_folio(page_list);
         list_del(&folio->lru);
 
         if (!folio_trylock(folio))
             goto keep;
 
         VM_BUG_ON_FOLIO(folio_test_active(folio), folio);
 
         nr_pages = folio_nr_pages(folio);
 
         /* Account the number of base pages */
         sc->nr_scanned += nr_pages;
 
         if (unlikely(!folio_evictable(folio)))
             goto activate_locked;
 
         if (!sc->may_unmap && folio_mapped(folio))
             goto keep_locked;
 
         /*
          * The number of dirty pages determines if a node is marked
          * reclaim_congested. kswapd will stall and start writing
          * folios if the tail of the LRU is all dirty unqueued folios.
          */
         folio_check_dirty_writeback(folio, &dirty, &writeback);
         if (dirty || writeback)
             stat->nr_dirty += nr_pages;
 
         if (dirty && !writeback)
             stat->nr_unqueued_dirty += nr_pages;
 
         /*
          * Treat this folio as congested if folios are cycling
          * through the LRU so quickly that the folios marked
          * for immediate reclaim are making it to the end of
          * the LRU a second time.
          */
         if (writeback && folio_test_reclaim(folio))
             stat->nr_congested += nr_pages;
 
         /*
          * If a folio at the tail of the LRU is under writeback, there
          * are three cases to consider.
          *
          * 1) If reclaim is encountering an excessive number
          *    of folios under writeback and this folio has both
          *    the writeback and reclaim flags set, then it
          *    indicates that folios are being queued for I/O but
          *    are being recycled through the LRU before the I/O
          *    can complete. Waiting on the folio itself risks an
          *    indefinite stall if it is impossible to writeback
          *    the folio due to I/O error or disconnected storage
          *    so instead note that the LRU is being scanned too
          *    quickly and the caller can stall after the folio
          *    list has been processed.
          *
          * 2) Global or new memcg reclaim encounters a folio that is
          *    not marked for immediate reclaim, or the caller does not
          *    have __GFP_FS (or __GFP_IO if it's simply going to swap,
          *    not to fs). In this case mark the folio for immediate
          *    reclaim and continue scanning.
          *
          *    Require may_enter_fs() because we would wait on fs, which
          *    may not have submitted I/O yet. And the loop driver might
          *    enter reclaim, and deadlock if it waits on a folio for
          *    which it is needed to do the write (loop masks off
          *    __GFP_IO|__GFP_FS for this reason); but more thought
          *    would probably show more reasons.
          *
          * 3) Legacy memcg encounters a folio that already has the
          *    reclaim flag set. memcg does not have any dirty folio
          *    throttling so we could easily OOM just because too many
          *    folios are in writeback and there is nothing else to
          *    reclaim. Wait for the writeback to complete.
          *
          * In cases 1) and 2) we activate the folios to get them out of
          * the way while we continue scanning for clean folios on the
          * inactive list and refilling from the active list. The
          * observation here is that waiting for disk writes is more
          * expensive than potentially causing reloads down the line.
          * Since they're marked for immediate reclaim, they won't put
          * memory pressure on the cache working set any longer than it
          * takes to write them to disk.
          */
         if (folio_test_writeback(folio)) {
             /* Case 1 above */
             if (current_is_kswapd() &&
                 folio_test_reclaim(folio) &&
                 test_bit(PGDAT_WRITEBACK, &pgdat->flags)) {
                 stat->nr_immediate += nr_pages;
                 goto activate_locked;
 
             /* Case 2 above */
             } else if (writeback_throttling_sane(sc) ||
                 !folio_test_reclaim(folio) ||
                 !may_enter_fs(folio, sc->gfp_mask)) {
                 /*
                  * This is slightly racy -
                  * folio_end_writeback() might have
                  * just cleared the reclaim flag, then
                  * setting the reclaim flag here ends up
                  * interpreted as the readahead flag - but
                  * that does not matter enough to care.
                  * What we do want is for this folio to
                  * have the reclaim flag set next time
                  * memcg reclaim reaches the tests above,
                  * so it will then wait for writeback to
                  * avoid OOM; and it's also appropriate
                  * in global reclaim.
                  */
                 folio_set_reclaim(folio);
                 stat->nr_writeback += nr_pages;
                 goto activate_locked;
 
             /* Case 3 above */
             } else {
                 folio_unlock(folio);
                 folio_wait_writeback(folio);
                 /* then go back and try same folio again */
                 list_add_tail(&folio->lru, page_list);
                 continue;
             }
         }
 
         if (!ignore_references)
             references = folio_check_references(folio, sc);
 
         switch (references) {
         case PAGEREF_ACTIVATE:
             goto activate_locked;
         case PAGEREF_KEEP:
             stat->nr_ref_keep += nr_pages;
             goto keep_locked;
         case PAGEREF_RECLAIM:
         case PAGEREF_RECLAIM_CLEAN:
             ; /* try to reclaim the folio below */
         }
 
         /*
          * Before reclaiming the folio, try to relocate
          * its contents to another node.
          */
         if (do_demote_pass &&
             (thp_migration_supported() || !folio_test_large(folio))) {
             list_add(&folio->lru, &demote_pages);
             folio_unlock(folio);
             continue;
         }
 
         /*
          * Anonymous process memory has backing store?
          * Try to allocate it some swap space here.
          * Lazyfree folio could be freed directly
          */
         if (folio_test_anon(folio) && folio_test_swapbacked(folio)) {
             if (!folio_test_swapcache(folio)) {
                 if (!(sc->gfp_mask & __GFP_IO))
                     goto keep_locked;
                 if (folio_maybe_dma_pinned(folio))
                     goto keep_locked;
                 if (folio_test_large(folio)) {
                     /* cannot split folio, skip it */
                     if (!can_split_folio(folio, NULL))
                         goto activate_locked;
                     /*
                      * Split folios without a PMD map right
                      * away. Chances are some or all of the
                      * tail pages can be freed without IO.
                      */
                     if (!folio_entire_mapcount(folio) &&
                         split_folio_to_list(folio,
                                 page_list))
                         goto activate_locked;
                 }
                 if (!add_to_swap(folio)) {
                     if (!folio_test_large(folio))
                         goto activate_locked_split;
                     /* Fallback to swap normal pages */
                     if (split_folio_to_list(folio,
                                 page_list))
                         goto activate_locked;
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
                     count_vm_event(THP_SWPOUT_FALLBACK);
 #endif
                     if (!add_to_swap(folio))
                         goto activate_locked_split;
                 }
             }
         } else if (folio_test_swapbacked(folio) &&
                folio_test_large(folio)) {
             /* Split shmem folio */
             if (split_folio_to_list(folio, page_list))
                 goto keep_locked;
         }
 
         /*
          * If the folio was split above, the tail pages will make
          * their own pass through this function and be accounted
          * then.
          */
         if ((nr_pages > 1) && !folio_test_large(folio)) {
             sc->nr_scanned -= (nr_pages - 1);
             nr_pages = 1;
         }
 
         /*
          * The folio is mapped into the page tables of one or more
          * processes. Try to unmap it here.
          */
         if (folio_mapped(folio)) {
             enum ttu_flags flags = TTU_BATCH_FLUSH;
             bool was_swapbacked = folio_test_swapbacked(folio);
 
             if (folio_test_pmd_mappable(folio))
                 flags |= TTU_SPLIT_HUGE_PMD;
 
             try_to_unmap(folio, flags);
             if (folio_mapped(folio)) {
                 stat->nr_unmap_fail += nr_pages;
                 if (!was_swapbacked &&
                     folio_test_swapbacked(folio))
                     stat->nr_lazyfree_fail += nr_pages;
                 goto activate_locked;
             }
         }
 
         mapping = folio_mapping(folio);
         if (folio_test_dirty(folio)) {
             /*
              * Only kswapd can writeback filesystem folios
              * to avoid risk of stack overflow. But avoid
              * injecting inefficient single-folio I/O into
              * flusher writeback as much as possible: only
              * write folios when we've encountered many
              * dirty folios, and when we've already scanned
              * the rest of the LRU for clean folios and see
              * the same dirty folios again (with the reclaim
              * flag set).
              */
             if (folio_is_file_lru(folio) &&
                 (!current_is_kswapd() ||
                  !folio_test_reclaim(folio) ||
                  !test_bit(PGDAT_DIRTY, &pgdat->flags))) {
                 /*
                  * Immediately reclaim when written back.
                  * Similar in principle to deactivate_page()
                  * except we already have the folio isolated
                  * and know it's dirty
                  */
                 node_stat_mod_folio(folio, NR_VMSCAN_IMMEDIATE,
                         nr_pages);
                 folio_set_reclaim(folio);
 
                 goto activate_locked;
             }
 
             if (references == PAGEREF_RECLAIM_CLEAN)
                 goto keep_locked;
             if (!may_enter_fs(folio, sc->gfp_mask))
                 goto keep_locked;
             if (!sc->may_writepage)
                 goto keep_locked;
 
             /*
              * Folio is dirty. Flush the TLB if a writable entry
              * potentially exists to avoid CPU writes after I/O
              * starts and then write it out here.
              */
             try_to_unmap_flush_dirty();
             switch (pageout(folio, mapping, &plug)) {
             case PAGE_KEEP:
                 goto keep_locked;
             case PAGE_ACTIVATE:
                 goto activate_locked;
             case PAGE_SUCCESS:
                 stat->nr_pageout += nr_pages;
 
                 if (folio_test_writeback(folio))
                     goto keep;
                 if (folio_test_dirty(folio))
                     goto keep;
 
                 /*
                  * A synchronous write - probably a ramdisk.  Go
                  * ahead and try to reclaim the folio.
                  */
                 if (!folio_trylock(folio))
                     goto keep;
                 if (folio_test_dirty(folio) ||
                     folio_test_writeback(folio))
                     goto keep_locked;
                 mapping = folio_mapping(folio);
                 fallthrough;
             case PAGE_CLEAN:
                 ; /* try to free the folio below */
             }
         }
 
         /*
          * If the folio has buffers, try to free the buffer
          * mappings associated with this folio. If we succeed
          * we try to free the folio as well.
          *
          * We do this even if the folio is dirty.
          * filemap_release_folio() does not perform I/O, but it
          * is possible for a folio to have the dirty flag set,
          * but it is actually clean (all its buffers are clean).
          * This happens if the buffers were written out directly,
          * with submit_bh(). ext3 will do this, as well as
          * the blockdev mapping.  filemap_release_folio() will
          * discover that cleanness and will drop the buffers
          * and mark the folio clean - it can be freed.
          *
          * Rarely, folios can have buffers and no ->mapping.
          * These are the folios which were not successfully
          * invalidated in truncate_cleanup_folio().  We try to
          * drop those buffers here and if that worked, and the
          * folio is no longer mapped into process address space
          * (refcount == 1) it can be freed.  Otherwise, leave
          * the folio on the LRU so it is swappable.
          */
         if (folio_has_private(folio)) {
             if (!filemap_release_folio(folio, sc->gfp_mask))
                 goto activate_locked;
             if (!mapping && folio_ref_count(folio) == 1) {
                 folio_unlock(folio);
                 if (folio_put_testzero(folio))
                     goto free_it;
                 else {
                     /*
                      * rare race with speculative reference.
                      * the speculative reference will free
                      * this folio shortly, so we may
                      * increment nr_reclaimed here (and
                      * leave it off the LRU).
                      */
                     nr_reclaimed += nr_pages;
                     continue;
                 }
             }
         }
 
         if (folio_test_anon(folio) && !folio_test_swapbacked(folio)) {
             /* follow __remove_mapping for reference */
             if (!folio_ref_freeze(folio, 1))
                 goto keep_locked;
             /*
              * The folio has only one reference left, which is
              * from the isolation. After the caller puts the
              * folio back on the lru and drops the reference, the
              * folio will be freed anyway. It doesn't matter
              * which lru it goes on. So we don't bother checking
              * the dirty flag here.
              */
             count_vm_events(PGLAZYFREED, nr_pages);
             count_memcg_folio_events(folio, PGLAZYFREED, nr_pages);
         } else if (!mapping || !__remove_mapping(mapping, folio, true,
                              sc->target_mem_cgroup))
             goto keep_locked;
 
         folio_unlock(folio);
 free_it:
         /*
          * Folio may get swapped out as a whole, need to account
          * all pages in it.
          */
         nr_reclaimed += nr_pages;
 
         /*
          * Is there need to periodically free_page_list? It would
          * appear not as the counts should be low
          */
         if (unlikely(folio_test_large(folio)))
             destroy_large_folio(folio);
         else
             list_add(&folio->lru, &free_pages);
         continue;
 
 activate_locked_split:
         /*
          * The tail pages that are failed to add into swap cache
          * reach here.  Fixup nr_scanned and nr_pages.
          */
         if (nr_pages > 1) {
             sc->nr_scanned -= (nr_pages - 1);
             nr_pages = 1;
         }
 activate_locked:
         /* Not a candidate for swapping, so reclaim swap space. */
         if (folio_test_swapcache(folio) &&
             (mem_cgroup_swap_full(&folio->page) ||
              folio_test_mlocked(folio)))
             try_to_free_swap(&folio->page);
         VM_BUG_ON_FOLIO(folio_test_active(folio), folio);
         if (!folio_test_mlocked(folio)) {
             int type = folio_is_file_lru(folio);
             folio_set_active(folio);
             stat->nr_activate[type] += nr_pages;
             count_memcg_folio_events(folio, PGACTIVATE, nr_pages);
         }
 keep_locked:
         folio_unlock(folio);
 keep:
         list_add(&folio->lru, &ret_pages);
         VM_BUG_ON_FOLIO(folio_test_lru(folio) ||
                 folio_test_unevictable(folio), folio);
     }
     /* 'page_list' is always empty here */
 
     /* Migrate folios selected for demotion */
     nr_reclaimed += demote_page_list(&demote_pages, pgdat);
     /* Folios that could not be demoted are still in @demote_pages */
     if (!list_empty(&demote_pages)) {
         /* Folios which weren't demoted go back on @page_list for retry: */
         list_splice_init(&demote_pages, page_list);
         do_demote_pass = false;
         goto retry;
     }
 
     pgactivate = stat->nr_activate[0] + stat->nr_activate[1];
 
     mem_cgroup_uncharge_list(&free_pages);
     try_to_unmap_flush();
     free_unref_page_list(&free_pages);
 
     list_splice(&ret_pages, page_list);
     count_vm_events(PGACTIVATE, pgactivate);
 
     if (plug)
         swap_write_unplug(plug);
     return nr_reclaimed;
 }
 
 unsigned int reclaim_clean_pages_from_list(struct zone *zone,
                         struct list_head *folio_list)
 {
     struct scan_control sc = {
         .gfp_mask = GFP_KERNEL,
         .may_unmap = 1,
     };
     struct reclaim_stat stat;
     unsigned int nr_reclaimed;
     struct folio *folio, *next;
     LIST_HEAD(clean_folios);
     unsigned int noreclaim_flag;
 
     list_for_each_entry_safe(folio, next, folio_list, lru) {
         if (!folio_test_hugetlb(folio) && folio_is_file_lru(folio) &&
             !folio_test_dirty(folio) && !__folio_test_movable(folio) &&
             !folio_test_unevictable(folio)) {
             folio_clear_active(folio);
             list_move(&folio->lru, &clean_folios);
         }
     }
 
     /*
      * We should be safe here since we are only dealing with file pages and
      * we are not kswapd and therefore cannot write dirty file pages. But
      * call memalloc_noreclaim_save() anyway, just in case these conditions
      * change in the future.
      */
     noreclaim_flag = memalloc_noreclaim_save();
     nr_reclaimed = shrink_page_list(&clean_folios, zone->zone_pgdat, &sc,
                     &stat, true);
     memalloc_noreclaim_restore(noreclaim_flag);
 
     list_splice(&clean_folios, folio_list);
     mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE,
                 -(long)nr_reclaimed);
     /*
      * Since lazyfree pages are isolated from file LRU from the beginning,
      * they will rotate back to anonymous LRU in the end if it failed to
      * discard so isolated count will be mismatched.
      * Compensate the isolated count for both LRU lists.
      */
     mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_ANON,
                 stat.nr_lazyfree_fail);
     mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE,
                 -(long)stat.nr_lazyfree_fail);
     return nr_reclaimed;
 }
 
 /*
  * Update LRU sizes after isolating pages. The LRU size updates must
  * be complete before mem_cgroup_update_lru_size due to a sanity check.
  */
 static __always_inline void update_lru_sizes(struct lruvec *lruvec,
             enum lru_list lru, unsigned long *nr_zone_taken)
 {
     int zid;
 
     for (zid = 0; zid < MAX_NR_ZONES; zid++) {
         if (!nr_zone_taken[zid])
             continue;
 
         update_lru_size(lruvec, lru, zid, -nr_zone_taken[zid]);
     }
 
 }
 
 /*
  * Isolating page from the lruvec to fill in @dst list by nr_to_scan times.
  *
  * lruvec->lru_lock is heavily contended.  Some of the functions that
  * shrink the lists perform better by taking out a batch of pages
  * and working on them outside the LRU lock.
  *
  * For pagecache intensive workloads, this function is the hottest
  * spot in the kernel (apart from copy_*_user functions).
  *
  * Lru_lock must be held before calling this function.
  *
  * @nr_to_scan: The number of eligible pages to look through on the list.
  * @lruvec: The LRU vector to pull pages from.
  * @dst:    The temp list to put pages on to.
  * @nr_scanned: The number of pages that were scanned.
  * @sc:     The scan_control struct for this reclaim session
  * @lru:    LRU list id for isolating
  *
  * returns how many pages were moved onto *@dst.
  */
 static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
         struct lruvec *lruvec, struct list_head *dst,
         unsigned long *nr_scanned, struct scan_control *sc,
         enum lru_list lru)
 {
     struct list_head *src = &lruvec->lists[lru];
     unsigned long nr_taken = 0;
     unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 };
     unsigned long nr_skipped[MAX_NR_ZONES] = { 0, };
     unsigned long skipped = 0;
     unsigned long scan, total_scan, nr_pages;
     LIST_HEAD(folios_skipped);
 
     total_scan = 0;
     scan = 0;
     while (scan < nr_to_scan && !list_empty(src)) {
         struct list_head *move_to = src;
         struct folio *folio;
 
         folio = lru_to_folio(src);
         prefetchw_prev_lru_folio(folio, src, flags);
 
         nr_pages = folio_nr_pages(folio);
         total_scan += nr_pages;
 
         if (folio_zonenum(folio) > sc->reclaim_idx) {
             nr_skipped[folio_zonenum(folio)] += nr_pages;
             move_to = &folios_skipped;
             goto move;
         }
 
         /*
          * Do not count skipped folios because that makes the function
          * return with no isolated folios if the LRU mostly contains
          * ineligible folios.  This causes the VM to not reclaim any
          * folios, triggering a premature OOM.
          * Account all pages in a folio.
          */
         scan += nr_pages;
 
         if (!folio_test_lru(folio))
             goto move;
         if (!sc->may_unmap && folio_mapped(folio))
             goto move;
 
         /*
          * Be careful not to clear the lru flag until after we're
          * sure the folio is not being freed elsewhere -- the
          * folio release code relies on it.
          */
         if (unlikely(!folio_try_get(folio)))
             goto move;
 
         if (!folio_test_clear_lru(folio)) {
             /* Another thread is already isolating this folio */
             folio_put(folio);
             goto move;
         }
 
         nr_taken += nr_pages;
         nr_zone_taken[folio_zonenum(folio)] += nr_pages;
         move_to = dst;
 move:
         list_move(&folio->lru, move_to);
     }
 
     /*
      * Splice any skipped folios to the start of the LRU list. Note that
      * this disrupts the LRU order when reclaiming for lower zones but
      * we cannot splice to the tail. If we did then the SWAP_CLUSTER_MAX
      * scanning would soon rescan the same folios to skip and waste lots
      * of cpu cycles.
      */
     if (!list_empty(&folios_skipped)) {
         int zid;
 
         list_splice(&folios_skipped, src);
         for (zid = 0; zid < MAX_NR_ZONES; zid++) {
             if (!nr_skipped[zid])
                 continue;
 
             __count_zid_vm_events(PGSCAN_SKIP, zid, nr_skipped[zid]);
             skipped += nr_skipped[zid];
         }
     }
     *nr_scanned = total_scan;
     trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan,
                     total_scan, skipped, nr_taken,
                     sc->may_unmap ? 0 : ISOLATE_UNMAPPED, lru);
     update_lru_sizes(lruvec, lru, nr_zone_taken);
     return nr_taken;
 }
 
 /**
  * folio_isolate_lru() - Try to isolate a folio from its LRU list.
  * @folio: Folio to isolate from its LRU list.
  *
  * Isolate a @folio from an LRU list and adjust the vmstat statistic
  * corresponding to whatever LRU list the folio was on.
  *
  * The folio will have its LRU flag cleared.  If it was found on the
  * active list, it will have the Active flag set.  If it was found on the
  * unevictable list, it will have the Unevictable flag set.  These flags
  * may need to be cleared by the caller before letting the page go.
  *
  * Context:
  *
  * (1) Must be called with an elevated refcount on the page. This is a
  *     fundamental difference from isolate_lru_pages() (which is called
  *     without a stable reference).
  * (2) The lru_lock must not be held.
  * (3) Interrupts must be enabled.
  *
  * Return: 0 if the folio was removed from an LRU list.
  * -EBUSY if the folio was not on an LRU list.
  */
 int folio_isolate_lru(struct folio *folio)
 {
     int ret = -EBUSY;
 
     VM_BUG_ON_FOLIO(!folio_ref_count(folio), folio);
 
     if (folio_test_clear_lru(folio)) {
         struct lruvec *lruvec;
 
         folio_get(folio);
         lruvec = folio_lruvec_lock_irq(folio);
         lruvec_del_folio(lruvec, folio);
         unlock_page_lruvec_irq(lruvec);
         ret = 0;
     }
 
     return ret;
 }
 
 /*
  * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
  * then get rescheduled. When there are massive number of tasks doing page
  * allocation, such sleeping direct reclaimers may keep piling up on each CPU,
  * the LRU list will go small and be scanned faster than necessary, leading to
  * unnecessary swapping, thrashing and OOM.
  */
 static int too_many_isolated(struct pglist_data *pgdat, int file,
         struct scan_control *sc)
 {
     unsigned long inactive, isolated;
     bool too_many;
 
     if (current_is_kswapd())
         return 0;
 
     if (!writeback_throttling_sane(sc))
         return 0;
 
     if (file) {
         inactive = node_page_state(pgdat, NR_INACTIVE_FILE);
         isolated = node_page_state(pgdat, NR_ISOLATED_FILE);
     } else {
         inactive = node_page_state(pgdat, NR_INACTIVE_ANON);
         isolated = node_page_state(pgdat, NR_ISOLATED_ANON);
     }
 
     /*
      * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
      * won't get blocked by normal direct-reclaimers, forming a circular
      * deadlock.
      */
     if ((sc->gfp_mask & (__GFP_IO | __GFP_FS)) == (__GFP_IO | __GFP_FS))
         inactive >>= 3;
 
     too_many = isolated > inactive;
 
     /* Wake up tasks throttled due to too_many_isolated. */
     if (!too_many)
         wake_throttle_isolated(pgdat);
 
     return too_many;
 }
 
 /*
  * move_pages_to_lru() moves folios from private @list to appropriate LRU list.
  * On return, @list is reused as a list of folios to be freed by the caller.
  *
  * Returns the number of pages moved to the given lruvec.
  */
 static unsigned int move_pages_to_lru(struct lruvec *lruvec,
                       struct list_head *list)
 {
     int nr_pages, nr_moved = 0;
     LIST_HEAD(folios_to_free);
 
     while (!list_empty(list)) {
         struct folio *folio = lru_to_folio(list);
 
         VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);
         list_del(&folio->lru);
         if (unlikely(!folio_evictable(folio))) {
             spin_unlock_irq(&lruvec->lru_lock);
             folio_putback_lru(folio);
             spin_lock_irq(&lruvec->lru_lock);
             continue;
         }
 
         /*
          * The folio_set_lru needs to be kept here for list integrity.
          * Otherwise:
          *   #0 move_pages_to_lru             #1 release_pages
          *   if (!folio_put_testzero())
          *                    if (folio_put_testzero())
          *                      !lru //skip lru_lock
          *     folio_set_lru()
          *     list_add(&folio->lru,)
          *                                        list_add(&folio->lru,)
          */
         folio_set_lru(folio);
 
         if (unlikely(folio_put_testzero(folio))) {
             __folio_clear_lru_flags(folio);
 
             if (unlikely(folio_test_large(folio))) {
                 spin_unlock_irq(&lruvec->lru_lock);
                 destroy_large_folio(folio);
                 spin_lock_irq(&lruvec->lru_lock);
             } else
                 list_add(&folio->lru, &folios_to_free);
 
             continue;
         }
 
         /*
          * All pages were isolated from the same lruvec (and isolation
          * inhibits memcg migration).
          */
         VM_BUG_ON_FOLIO(!folio_matches_lruvec(folio, lruvec), folio);
         lruvec_add_folio(lruvec, folio);
         nr_pages = folio_nr_pages(folio);
         nr_moved += nr_pages;
         if (folio_test_active(folio))
             workingset_age_nonresident(lruvec, nr_pages);
     }
 
     /*
      * To save our caller's stack, now use input list for pages to free.
      */
     list_splice(&folios_to_free, list);
 
     return nr_moved;
 }
 
 /*
  * If a kernel thread (such as nfsd for loop-back mounts) services a backing
  * device by writing to the page cache it sets PF_LOCAL_THROTTLE. In this case
  * we should not throttle.  Otherwise it is safe to do so.
  */
 static int current_may_throttle(void)
 {
     return !(current->flags & PF_LOCAL_THROTTLE);
 }
 
 /*
  * shrink_inactive_list() is a helper for shrink_node().  It returns the number
  * of reclaimed pages
  */
 static unsigned long
 shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
              struct scan_control *sc, enum lru_list lru)
 {
     LIST_HEAD(page_list);
     unsigned long nr_scanned;
     unsigned int nr_reclaimed = 0;
     unsigned long nr_taken;
     struct reclaim_stat stat;
     bool file = is_file_lru(lru);
     enum vm_event_item item;
     struct pglist_data *pgdat = lruvec_pgdat(lruvec);
     bool stalled = false;
 
     while (unlikely(too_many_isolated(pgdat, file, sc))) {
         if (stalled)
             return 0;
 
         /* wait a bit for the reclaimer. */
         stalled = true;
         reclaim_throttle(pgdat, VMSCAN_THROTTLE_ISOLATED);
 
         /* We are about to die and free our memory. Return now. */
         if (fatal_signal_pending(current))
             return SWAP_CLUSTER_MAX;
     }
 
     lru_add_drain();
 
     spin_lock_irq(&lruvec->lru_lock);
 
     nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
                      &nr_scanned, sc, lru);
 
     __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
     item = current_is_kswapd() ? PGSCAN_KSWAPD : PGSCAN_DIRECT;
     if (!cgroup_reclaim(sc))
         __count_vm_events(item, nr_scanned);
     __count_memcg_events(lruvec_memcg(lruvec), item, nr_scanned);
     __count_vm_events(PGSCAN_ANON + file, nr_scanned);
 
     spin_unlock_irq(&lruvec->lru_lock);
 
     if (nr_taken == 0)
         return 0;
 
     nr_reclaimed = shrink_page_list(&page_list, pgdat, sc, &stat, false);
 
     spin_lock_irq(&lruvec->lru_lock);
     move_pages_to_lru(lruvec, &page_list);
 
     __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
     item = current_is_kswapd() ? PGSTEAL_KSWAPD : PGSTEAL_DIRECT;
     if (!cgroup_reclaim(sc))
         __count_vm_events(item, nr_reclaimed);
     __count_memcg_events(lruvec_memcg(lruvec), item, nr_reclaimed);
     __count_vm_events(PGSTEAL_ANON + file, nr_reclaimed);
     spin_unlock_irq(&lruvec->lru_lock);
 
     lru_note_cost(lruvec, file, stat.nr_pageout);
     mem_cgroup_uncharge_list(&page_list);
     free_unref_page_list(&page_list);
 
     /*
      * If dirty pages are scanned that are not queued for IO, it
      * implies that flushers are not doing their job. This can
      * happen when memory pressure pushes dirty pages to the end of
      * the LRU before the dirty limits are breached and the dirty
      * data has expired. It can also happen when the proportion of
      * dirty pages grows not through writes but through memory
      * pressure reclaiming all the clean cache. And in some cases,
      * the flushers simply cannot keep up with the allocation
      * rate. Nudge the flusher threads in case they are asleep.
      */
     if (stat.nr_unqueued_dirty == nr_taken)
         wakeup_flusher_threads(WB_REASON_VMSCAN);
 
     sc->nr.dirty += stat.nr_dirty;
     sc->nr.congested += stat.nr_congested;
     sc->nr.unqueued_dirty += stat.nr_unqueued_dirty;
     sc->nr.writeback += stat.nr_writeback;
     sc->nr.immediate += stat.nr_immediate;
     sc->nr.taken += nr_taken;
     if (file)
         sc->nr.file_taken += nr_taken;
 
     trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
             nr_scanned, nr_reclaimed, &stat, sc->priority, file);
     return nr_reclaimed;
 }
 
 /*
  * shrink_active_list() moves folios from the active LRU to the inactive LRU.
  *
  * We move them the other way if the folio is referenced by one or more
  * processes.
  *
  * If the folios are mostly unmapped, the processing is fast and it is
  * appropriate to hold lru_lock across the whole operation.  But if
  * the folios are mapped, the processing is slow (folio_referenced()), so
  * we should drop lru_lock around each folio.  It's impossible to balance
  * this, so instead we remove the folios from the LRU while processing them.
  * It is safe to rely on the active flag against the non-LRU folios in here
  * because nobody will play with that bit on a non-LRU folio.
  *
  * The downside is that we have to touch folio->_refcount against each folio.
  * But we had to alter folio->flags anyway.
  */
 static void shrink_active_list(unsigned long nr_to_scan,
                    struct lruvec *lruvec,
                    struct scan_control *sc,
                    enum lru_list lru)
 {
     unsigned long nr_taken;
     unsigned long nr_scanned;
     unsigned long vm_flags;
     LIST_HEAD(l_hold);  /* The folios which were snipped off */
     LIST_HEAD(l_active);
     LIST_HEAD(l_inactive);
     unsigned nr_deactivate, nr_activate;
     unsigned nr_rotated = 0;
     int file = is_file_lru(lru);
     struct pglist_data *pgdat = lruvec_pgdat(lruvec);
 
     lru_add_drain();
 
     spin_lock_irq(&lruvec->lru_lock);
 
     nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
                      &nr_scanned, sc, lru);
 
     __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
 
     if (!cgroup_reclaim(sc))
         __count_vm_events(PGREFILL, nr_scanned);
     __count_memcg_events(lruvec_memcg(lruvec), PGREFILL, nr_scanned);
 
     spin_unlock_irq(&lruvec->lru_lock);
 
     while (!list_empty(&l_hold)) {
         struct folio *folio;
 
         cond_resched();
         folio = lru_to_folio(&l_hold);
         list_del(&folio->lru);
 
         if (unlikely(!folio_evictable(folio))) {
             folio_putback_lru(folio);
             continue;
         }
 
         if (unlikely(buffer_heads_over_limit)) {
             if (folio_test_private(folio) && folio_trylock(folio)) {
                 if (folio_test_private(folio))
                     filemap_release_folio(folio, 0);
                 folio_unlock(folio);
             }
         }
 
         /* Referenced or rmap lock contention: rotate */
         if (folio_referenced(folio, 0, sc->target_mem_cgroup,
                      &vm_flags) != 0) {
             /*
              * Identify referenced, file-backed active folios and
              * give them one more trip around the active list. So
              * that executable code get better chances to stay in
              * memory under moderate memory pressure.  Anon folios
              * are not likely to be evicted by use-once streaming
              * IO, plus JVM can create lots of anon VM_EXEC folios,
              * so we ignore them here.
              */
             if ((vm_flags & VM_EXEC) && folio_is_file_lru(folio)) {
                 nr_rotated += folio_nr_pages(folio);
                 list_add(&folio->lru, &l_active);
                 continue;
             }
         }
 
         folio_clear_active(folio);  /* we are de-activating */
         folio_set_workingset(folio);
         list_add(&folio->lru, &l_inactive);
     }
 
     /*
      * Move folios back to the lru list.
      */
     spin_lock_irq(&lruvec->lru_lock);
 
     nr_activate = move_pages_to_lru(lruvec, &l_active);
     nr_deactivate = move_pages_to_lru(lruvec, &l_inactive);
     /* Keep all free folios in l_active list */
     list_splice(&l_inactive, &l_active);
 
     __count_vm_events(PGDEACTIVATE, nr_deactivate);
     __count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE, nr_deactivate);
 
     __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
     spin_unlock_irq(&lruvec->lru_lock);
 
     mem_cgroup_uncharge_list(&l_active);
     free_unref_page_list(&l_active);
     trace_mm_vmscan_lru_shrink_active(pgdat->node_id, nr_taken, nr_activate,
             nr_deactivate, nr_rotated, sc->priority, file);
 }
 
 static unsigned int reclaim_page_list(struct list_head *page_list,
                       struct pglist_data *pgdat)
 {
     struct reclaim_stat dummy_stat;
     unsigned int nr_reclaimed;
     struct folio *folio;
     struct scan_control sc = {
         .gfp_mask = GFP_KERNEL,
         .may_writepage = 1,
         .may_unmap = 1,
         .may_swap = 1,
         .no_demotion = 1,
     };
 
     nr_reclaimed = shrink_page_list(page_list, pgdat, &sc, &dummy_stat, false);
     while (!list_empty(page_list)) {
         folio = lru_to_folio(page_list);
         list_del(&folio->lru);
         folio_putback_lru(folio);
     }
 
     return nr_reclaimed;
 }
 
 unsigned long reclaim_pages(struct list_head *folio_list)
 {
     int nid;
     unsigned int nr_reclaimed = 0;
     LIST_HEAD(node_folio_list);
     unsigned int noreclaim_flag;
 
     if (list_empty(folio_list))
         return nr_reclaimed;
 
     noreclaim_flag = memalloc_noreclaim_save();
 
     nid = folio_nid(lru_to_folio(folio_list));
     do {
         struct folio *folio = lru_to_folio(folio_list);
 
         if (nid == folio_nid(folio)) {
             folio_clear_active(folio);
             list_move(&folio->lru, &node_folio_list);
             continue;
         }
 
         nr_reclaimed += reclaim_page_list(&node_folio_list, NODE_DATA(nid));
         nid = folio_nid(lru_to_folio(folio_list));
     } while (!list_empty(folio_list));
 
     nr_reclaimed += reclaim_page_list(&node_folio_list, NODE_DATA(nid));
 
     memalloc_noreclaim_restore(noreclaim_flag);
 
     return nr_reclaimed;
 }
 
 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
                  struct lruvec *lruvec, struct scan_control *sc)
 {
     if (is_active_lru(lru)) {
         if (sc->may_deactivate & (1 << is_file_lru(lru)))
             shrink_active_list(nr_to_scan, lruvec, sc, lru);
         else
             sc->skipped_deactivate = 1;
         return 0;
     }
 
     return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
 }
 
 /*
  * The inactive anon list should be small enough that the VM never has
  * to do too much work.
  *
  * The inactive file list should be small enough to leave most memory
  * to the established workingset on the scan-resistant active list,
  * but large enough to avoid thrashing the aggregate readahead window.
  *
  * Both inactive lists should also be large enough that each inactive
  * page has a chance to be referenced again before it is reclaimed.
  *
  * If that fails and refaulting is observed, the inactive list grows.
  *
  * The inactive_ratio is the target ratio of ACTIVE to INACTIVE pages
  * on this LRU, maintained by the pageout code. An inactive_ratio
  * of 3 means 3:1 or 25% of the pages are kept on the inactive list.
  *
  * total     target    max
  * memory    ratio     inactive
  * -------------------------------------
  *   10MB       1         5MB
  *  100MB       1        50MB
  *    1GB       3       250MB
  *   10GB      10       0.9GB
  *  100GB      31         3GB
  *    1TB     101        10GB
  *   10TB     320        32GB
  */
 static bool inactive_is_low(struct lruvec *lruvec, enum lru_list inactive_lru)
 {
     enum lru_list active_lru = inactive_lru + LRU_ACTIVE;
     unsigned long inactive, active;
     unsigned long inactive_ratio;
     unsigned long gb;
 
     inactive = lruvec_page_state(lruvec, NR_LRU_BASE + inactive_lru);
     active = lruvec_page_state(lruvec, NR_LRU_BASE + active_lru);
 
     gb = (inactive + active) >> (30 - PAGE_SHIFT);
     if (gb)
         inactive_ratio = int_sqrt(10 * gb);
     else
         inactive_ratio = 1;
 
     return inactive * inactive_ratio < active;
 }
 
 enum scan_balance {
     SCAN_EQUAL,
     SCAN_FRACT,
     SCAN_ANON,
     SCAN_FILE,
 };
 
 /*
  * Determine how aggressively the anon and file LRU lists should be
  * scanned.
  *
  * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
  * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
  */
 static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
                unsigned long *nr)
 {
     struct pglist_data *pgdat = lruvec_pgdat(lruvec);
     struct mem_cgroup *memcg = lruvec_memcg(lruvec);
     unsigned long anon_cost, file_cost, total_cost;
     int swappiness = mem_cgroup_swappiness(memcg);
     u64 fraction[ANON_AND_FILE];
     u64 denominator = 0;    /* gcc */
     enum scan_balance scan_balance;
     unsigned long ap, fp;
     enum lru_list lru;
 
     /* If we have no swap space, do not bother scanning anon pages. */
     if (!sc->may_swap || !can_reclaim_anon_pages(memcg, pgdat->node_id, sc)) {
         scan_balance = SCAN_FILE;
         goto out;
     }
 
     /*
      * Global reclaim will swap to prevent OOM even with no
      * swappiness, but memcg users want to use this knob to
      * disable swapping for individual groups completely when
      * using the memory controller's swap limit feature would be
      * too expensive.
      */
     if (cgroup_reclaim(sc) && !swappiness) {
         scan_balance = SCAN_FILE;
         goto out;
     }
 
     /*
      * Do not apply any pressure balancing cleverness when the
      * system is close to OOM, scan both anon and file equally
      * (unless the swappiness setting disagrees with swapping).
      */
     if (!sc->priority && swappiness) {
         scan_balance = SCAN_EQUAL;
         goto out;
     }
 
     /*
      * If the system is almost out of file pages, force-scan anon.
      */
     if (sc->file_is_tiny) {
         scan_balance = SCAN_ANON;
         goto out;
     }
 
     /*
      * If there is enough inactive page cache, we do not reclaim
      * anything from the anonymous working right now.
      */
     if (sc->cache_trim_mode) {
         scan_balance = SCAN_FILE;
         goto out;
     }
 
     scan_balance = SCAN_FRACT;
     /*
      * Calculate the pressure balance between anon and file pages.
      *
      * The amount of pressure we put on each LRU is inversely
      * proportional to the cost of reclaiming each list, as
      * determined by the share of pages that are refaulting, times
      * the relative IO cost of bringing back a swapped out
      * anonymous page vs reloading a filesystem page (swappiness).
      *
      * Although we limit that influence to ensure no list gets
      * left behind completely: at least a third of the pressure is
      * applied, before swappiness.
      *
      * With swappiness at 100, anon and file have equal IO cost.
      */
     total_cost = sc->anon_cost + sc->file_cost;
     anon_cost = total_cost + sc->anon_cost;
     file_cost = total_cost + sc->file_cost;
     total_cost = anon_cost + file_cost;
 
     ap = swappiness * (total_cost + 1);
     ap /= anon_cost + 1;
 
     fp = (200 - swappiness) * (total_cost + 1);
     fp /= file_cost + 1;
 
     fraction[0] = ap;
     fraction[1] = fp;
     denominator = ap + fp;
 out:
     for_each_evictable_lru(lru) {
         int file = is_file_lru(lru);
         unsigned long lruvec_size;
         unsigned long low, min;
         unsigned long scan;
 
         lruvec_size = lruvec_lru_size(lruvec, lru, sc->reclaim_idx);
         mem_cgroup_protection(sc->target_mem_cgroup, memcg,
                       &min, &low);
 
         if (min || low) {
             /*
              * Scale a cgroup's reclaim pressure by proportioning
              * its current usage to its memory.low or memory.min
              * setting.
              *
              * This is important, as otherwise scanning aggression
              * becomes extremely binary -- from nothing as we
              * approach the memory protection threshold, to totally
              * nominal as we exceed it.  This results in requiring
              * setting extremely liberal protection thresholds. It
              * also means we simply get no protection at all if we
              * set it too low, which is not ideal.
              *
              * If there is any protection in place, we reduce scan
              * pressure by how much of the total memory used is
              * within protection thresholds.
              *
              * There is one special case: in the first reclaim pass,
              * we skip over all groups that are within their low
              * protection. If that fails to reclaim enough pages to
              * satisfy the reclaim goal, we come back and override
              * the best-effort low protection. However, we still
              * ideally want to honor how well-behaved groups are in
              * that case instead of simply punishing them all
              * equally. As such, we reclaim them based on how much
              * memory they are using, reducing the scan pressure
              * again by how much of the total memory used is under
              * hard protection.
              */
             unsigned long cgroup_size = mem_cgroup_size(memcg);
             unsigned long protection;
 
             /* memory.low scaling, make sure we retry before OOM */
             if (!sc->memcg_low_reclaim && low > min) {
                 protection = low;
                 sc->memcg_low_skipped = 1;
             } else {
                 protection = min;
             }
 
             /* Avoid TOCTOU with earlier protection check */
             cgroup_size = max(cgroup_size, protection);
 
             scan = lruvec_size - lruvec_size * protection /
                 (cgroup_size + 1);
 
             /*
              * Minimally target SWAP_CLUSTER_MAX pages to keep
              * reclaim moving forwards, avoiding decrementing
              * sc->priority further than desirable.
              */
             scan = max(scan, SWAP_CLUSTER_MAX);
         } else {
             scan = lruvec_size;
         }
 
         scan >>= sc->priority;
 
         /*
          * If the cgroup's already been deleted, make sure to
          * scrape out the remaining cache.
          */
         if (!scan && !mem_cgroup_online(memcg))
             scan = min(lruvec_size, SWAP_CLUSTER_MAX);
 
         switch (scan_balance) {
         case SCAN_EQUAL:
             /* Scan lists relative to size */
             break;
         case SCAN_FRACT:
             /*
              * Scan types proportional to swappiness and
              * their relative recent reclaim efficiency.
              * Make sure we don't miss the last page on
              * the offlined memory cgroups because of a
              * round-off error.
              */
             scan = mem_cgroup_online(memcg) ?
                    div64_u64(scan * fraction[file], denominator) :
                    DIV64_U64_ROUND_UP(scan * fraction[file],
                           denominator);
             break;
         case SCAN_FILE:
         case SCAN_ANON:
             /* Scan one type exclusively */
             if ((scan_balance == SCAN_FILE) != file)
                 scan = 0;
             break;
         default:
             /* Look ma, no brain */
             BUG();
         }
 
         nr[lru] = scan;
     }
 }
 
 /*
  * Anonymous LRU management is a waste if there is
  * ultimately no way to reclaim the memory.
  */
 static bool can_age_anon_pages(struct pglist_data *pgdat,
                    struct scan_control *sc)
 {
     /* Aging the anon LRU is valuable if swap is present: */
     if (total_swap_pages > 0)
         return true;
 
     /* Also valuable if anon pages can be demoted: */
     return can_demote(pgdat->node_id, sc);
 }
 
 static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 {
     unsigned long nr[NR_LRU_LISTS];
     unsigned long targets[NR_LRU_LISTS];
     unsigned long nr_to_scan;
     enum lru_list lru;
     unsigned long nr_reclaimed = 0;
     unsigned long nr_to_reclaim = sc->nr_to_reclaim;
     struct blk_plug plug;
     bool scan_adjusted;
 
     get_scan_count(lruvec, sc, nr);
 
     /* Record the original scan target for proportional adjustments later */
     memcpy(targets, nr, sizeof(nr));
 
     /*
      * Global reclaiming within direct reclaim at DEF_PRIORITY is a normal
      * event that can occur when there is little memory pressure e.g.
      * multiple streaming readers/writers. Hence, we do not abort scanning
      * when the requested number of pages are reclaimed when scanning at
      * DEF_PRIORITY on the assumption that the fact we are direct
      * reclaiming implies that kswapd is not keeping up and it is best to
      * do a batch of work at once. For memcg reclaim one check is made to
      * abort proportional reclaim if either the file or anon lru has already
      * dropped to zero at the first pass.
      */
     scan_adjusted = (!cgroup_reclaim(sc) && !current_is_kswapd() &&
              sc->priority == DEF_PRIORITY);
 
     blk_start_plug(&plug);
     while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
                     nr[LRU_INACTIVE_FILE]) {
         unsigned long nr_anon, nr_file, percentage;
         unsigned long nr_scanned;
 
         for_each_evictable_lru(lru) {
             if (nr[lru]) {
                 nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
                 nr[lru] -= nr_to_scan;
 
                 nr_reclaimed += shrink_list(lru, nr_to_scan,
                                 lruvec, sc);
             }
         }
 
         cond_resched();
 
         if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
             continue;
 
         /*
          * For kswapd and memcg, reclaim at least the number of pages
          * requested. Ensure that the anon and file LRUs are scanned
          * proportionally what was requested by get_scan_count(). We
          * stop reclaiming one LRU and reduce the amount scanning
          * proportional to the original scan target.
          */
         nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE];
         nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON];
 
         /*
          * It's just vindictive to attack the larger once the smaller
          * has gone to zero.  And given the way we stop scanning the
          * smaller below, this makes sure that we only make one nudge
          * towards proportionality once we've got nr_to_reclaim.
          */
         if (!nr_file || !nr_anon)
             break;
 
         if (nr_file > nr_anon) {
             unsigned long scan_target = targets[LRU_INACTIVE_ANON] +
                         targets[LRU_ACTIVE_ANON] + 1;
             lru = LRU_BASE;
             percentage = nr_anon * 100 / scan_target;
         } else {
             unsigned long scan_target = targets[LRU_INACTIVE_FILE] +
                         targets[LRU_ACTIVE_FILE] + 1;
             lru = LRU_FILE;
             percentage = nr_file * 100 / scan_target;
         }
 
         /* Stop scanning the smaller of the LRU */
         nr[lru] = 0;
         nr[lru + LRU_ACTIVE] = 0;
 
         /*
          * Recalculate the other LRU scan count based on its original
          * scan target and the percentage scanning already complete
          */
         lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
         nr_scanned = targets[lru] - nr[lru];
         nr[lru] = targets[lru] * (100 - percentage) / 100;
         nr[lru] -= min(nr[lru], nr_scanned);
 
         lru += LRU_ACTIVE;
         nr_scanned = targets[lru] - nr[lru];
         nr[lru] = targets[lru] * (100 - percentage) / 100;
         nr[lru] -= min(nr[lru], nr_scanned);
 
         scan_adjusted = true;
     }
     blk_finish_plug(&plug);
     sc->nr_reclaimed += nr_reclaimed;
 
     /*
      * Even if we did not try to evict anon pages at all, we want to
      * rebalance the anon lru active/inactive ratio.
      */
     if (can_age_anon_pages(lruvec_pgdat(lruvec), sc) &&
         inactive_is_low(lruvec, LRU_INACTIVE_ANON))
         shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
                    sc, LRU_ACTIVE_ANON);
 }
 
 /* Use reclaim/compaction for costly allocs or under memory pressure */
 static bool in_reclaim_compaction(struct scan_control *sc)
 {
     if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
             (sc->order > PAGE_ALLOC_COSTLY_ORDER ||
              sc->priority < DEF_PRIORITY - 2))
         return true;
 
     return false;
 }
 
 /*
  * Reclaim/compaction is used for high-order allocation requests. It reclaims
  * order-0 pages before compacting the zone. should_continue_reclaim() returns
  * true if more pages should be reclaimed such that when the page allocator
  * calls try_to_compact_pages() that it will have enough free pages to succeed.
  * It will give up earlier than that if there is difficulty reclaiming pages.
  */
 static inline bool should_continue_reclaim(struct pglist_data *pgdat,
                     unsigned long nr_reclaimed,
                     struct scan_control *sc)
 {
     unsigned long pages_for_compaction;
     unsigned long inactive_lru_pages;
     int z;
 
     /* If not in reclaim/compaction mode, stop */
     if (!in_reclaim_compaction(sc))
         return false;
 
     /*
      * Stop if we failed to reclaim any pages from the last SWAP_CLUSTER_MAX
      * number of pages that were scanned. This will return to the caller
      * with the risk reclaim/compaction and the resulting allocation attempt
      * fails. In the past we have tried harder for __GFP_RETRY_MAYFAIL
      * allocations through requiring that the full LRU list has been scanned
      * first, by assuming that zero delta of sc->nr_scanned means full LRU
      * scan, but that approximation was wrong, and there were corner cases
      * where always a non-zero amount of pages were scanned.
      */
     if (!nr_reclaimed)
         return false;
 
     /* If compaction would go ahead or the allocation would succeed, stop */
     for (z = 0; z <= sc->reclaim_idx; z++) {
         struct zone *zone = &pgdat->node_zones[z];
         if (!managed_zone(zone))
             continue;
 
         switch (compaction_suitable(zone, sc->order, 0, sc->reclaim_idx)) {
         case COMPACT_SUCCESS:
         case COMPACT_CONTINUE:
             return false;
         default:
             /* check next zone */
             ;
         }
     }
 
     /*
      * If we have not reclaimed enough pages for compaction and the
      * inactive lists are large enough, continue reclaiming
      */
     pages_for_compaction = compact_gap(sc->order);
     inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
     if (can_reclaim_anon_pages(NULL, pgdat->node_id, sc))
         inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
 
     return inactive_lru_pages > pages_for_compaction;
 }
 
 static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
 {
     struct mem_cgroup *target_memcg = sc->target_mem_cgroup;
     struct mem_cgroup *memcg;
 
     memcg = mem_cgroup_iter(target_memcg, NULL, NULL);
     do {
         struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
         unsigned long reclaimed;
         unsigned long scanned;
 
         /*
          * This loop can become CPU-bound when target memcgs
          * aren't eligible for reclaim - either because they
          * don't have any reclaimable pages, or because their
          * memory is explicitly protected. Avoid soft lockups.
          */
         cond_resched();
 
         mem_cgroup_calculate_protection(target_memcg, memcg);
 
         if (mem_cgroup_below_min(memcg)) {
             /*
              * Hard protection.
              * If there is no reclaimable memory, OOM.
              */
             continue;
         } else if (mem_cgroup_below_low(memcg)) {
             /*
              * Soft protection.
              * Respect the protection only as long as
              * there is an unprotected supply
              * of reclaimable memory from other cgroups.
              */
             if (!sc->memcg_low_reclaim) {
                 sc->memcg_low_skipped = 1;
                 continue;
             }
             memcg_memory_event(memcg, MEMCG_LOW);
         }
 
         reclaimed = sc->nr_reclaimed;
         scanned = sc->nr_scanned;
 
         shrink_lruvec(lruvec, sc);
 
         shrink_slab(sc->gfp_mask, pgdat->node_id, memcg,
                 sc->priority);
 
         /* Record the group's reclaim efficiency */
         if (!sc->proactive)
             vmpressure(sc->gfp_mask, memcg, false,
                    sc->nr_scanned - scanned,
                    sc->nr_reclaimed - reclaimed);
 
     } while ((memcg = mem_cgroup_iter(target_memcg, memcg, NULL)));
 }
 
 static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
 {
     struct reclaim_state *reclaim_state = current->reclaim_state;
     unsigned long nr_reclaimed, nr_scanned;
     struct lruvec *target_lruvec;
     bool reclaimable = false;
     unsigned long file;
 
     target_lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup, pgdat);
 
 again:
     /*
      * Flush the memory cgroup stats, so that we read accurate per-memcg
      * lruvec stats for heuristics.
      */
     mem_cgroup_flush_stats();
 
     memset(&sc->nr, 0, sizeof(sc->nr));
 
     nr_reclaimed = sc->nr_reclaimed;
     nr_scanned = sc->nr_scanned;
 
     /*
      * Determine the scan balance between anon and file LRUs.
      */
     spin_lock_irq(&target_lruvec->lru_lock);
     sc->anon_cost = target_lruvec->anon_cost;
     sc->file_cost = target_lruvec->file_cost;
     spin_unlock_irq(&target_lruvec->lru_lock);
 
     /*
      * Target desirable inactive:active list ratios for the anon
      * and file LRU lists.
      */
     if (!sc->force_deactivate) {
         unsigned long refaults;
 
         refaults = lruvec_page_state(target_lruvec,
                 WORKINGSET_ACTIVATE_ANON);
         if (refaults != target_lruvec->refaults[0] ||
             inactive_is_low(target_lruvec, LRU_INACTIVE_ANON))
             sc->may_deactivate |= DEACTIVATE_ANON;
         else
             sc->may_deactivate &= ~DEACTIVATE_ANON;
 
         /*
          * When refaults are being observed, it means a new
          * workingset is being established. Deactivate to get
          * rid of any stale active pages quickly.
          */
         refaults = lruvec_page_state(target_lruvec,
                 WORKINGSET_ACTIVATE_FILE);
         if (refaults != target_lruvec->refaults[1] ||
             inactive_is_low(target_lruvec, LRU_INACTIVE_FILE))
             sc->may_deactivate |= DEACTIVATE_FILE;
         else
             sc->may_deactivate &= ~DEACTIVATE_FILE;
     } else
         sc->may_deactivate = DEACTIVATE_ANON | DEACTIVATE_FILE;
 
     /*
      * If we have plenty of inactive file pages that aren't
      * thrashing, try to reclaim those first before touching
      * anonymous pages.
      */
     file = lruvec_page_state(target_lruvec, NR_INACTIVE_FILE);
     if (file >> sc->priority && !(sc->may_deactivate & DEACTIVATE_FILE))
         sc->cache_trim_mode = 1;
     else
         sc->cache_trim_mode = 0;
 
     /*
      * Prevent the reclaimer from falling into the cache trap: as
      * cache pages start out inactive, every cache fault will tip
      * the scan balance towards the file LRU.  And as the file LRU
      * shrinks, so does the window for rotation from references.
      * This means we have a runaway feedback loop where a tiny
      * thrashing file LRU becomes infinitely more attractive than
      * anon pages.  Try to detect this based on file LRU size.
      */
     if (!cgroup_reclaim(sc)) {
         unsigned long total_high_wmark = 0;
         unsigned long free, anon;
         int z;
 
         free = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
         file = node_page_state(pgdat, NR_ACTIVE_FILE) +
                node_page_state(pgdat, NR_INACTIVE_FILE);
 
         for (z = 0; z < MAX_NR_ZONES; z++) {
             struct zone *zone = &pgdat->node_zones[z];
             if (!managed_zone(zone))
                 continue;
 
             total_high_wmark += high_wmark_pages(zone);
         }
 
         /*
          * Consider anon: if that's low too, this isn't a
          * runaway file reclaim problem, but rather just
          * extreme pressure. Reclaim as per usual then.
          */
         anon = node_page_state(pgdat, NR_INACTIVE_ANON);
 
         sc->file_is_tiny =
             file + free <= total_high_wmark &&
             !(sc->may_deactivate & DEACTIVATE_ANON) &&
             anon >> sc->priority;
     }
 
     shrink_node_memcgs(pgdat, sc);
 
     if (reclaim_state) {
         sc->nr_reclaimed += reclaim_state->reclaimed_slab;
         reclaim_state->reclaimed_slab = 0;
     }
 
     /* Record the subtree's reclaim efficiency */
     if (!sc->proactive)
         vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true,
                sc->nr_scanned - nr_scanned,
                sc->nr_reclaimed - nr_reclaimed);
 
     if (sc->nr_reclaimed - nr_reclaimed)
         reclaimable = true;
 
     if (current_is_kswapd()) {
         /*
          * If reclaim is isolating dirty pages under writeback,
          * it implies that the long-lived page allocation rate
          * is exceeding the page laundering rate. Either the
          * global limits are not being effective at throttling
          * processes due to the page distribution throughout
          * zones or there is heavy usage of a slow backing
          * device. The only option is to throttle from reclaim
          * context which is not ideal as there is no guarantee
          * the dirtying process is throttled in the same way
          * balance_dirty_pages() manages.
          *
          * Once a node is flagged PGDAT_WRITEBACK, kswapd will
          * count the number of pages under pages flagged for
          * immediate reclaim and stall if any are encountered
          * in the nr_immediate check below.
          */
         if (sc->nr.writeback && sc->nr.writeback == sc->nr.taken)
             set_bit(PGDAT_WRITEBACK, &pgdat->flags);
 
         /* Allow kswapd to start writing pages during reclaim.*/
         if (sc->nr.unqueued_dirty == sc->nr.file_taken)
             set_bit(PGDAT_DIRTY, &pgdat->flags);
 
         /*
          * If kswapd scans pages marked for immediate
          * reclaim and under writeback (nr_immediate), it
          * implies that pages are cycling through the LRU
          * faster than they are written so forcibly stall
          * until some pages complete writeback.
          */
         if (sc->nr.immediate)
             reclaim_throttle(pgdat, VMSCAN_THROTTLE_WRITEBACK);
     }
 
     /*
      * Tag a node/memcg as congested if all the dirty pages were marked
      * for writeback and immediate reclaim (counted in nr.congested).
      *
      * Legacy memcg will stall in page writeback so avoid forcibly
      * stalling in reclaim_throttle().
      */
     if ((current_is_kswapd() ||
          (cgroup_reclaim(sc) && writeback_throttling_sane(sc))) &&
         sc->nr.dirty && sc->nr.dirty == sc->nr.congested)
         set_bit(LRUVEC_CONGESTED, &target_lruvec->flags);
 
     /*
      * Stall direct reclaim for IO completions if the lruvec is
      * node is congested. Allow kswapd to continue until it
      * starts encountering unqueued dirty pages or cycling through
      * the LRU too quickly.
      */
     if (!current_is_kswapd() && current_may_throttle() &&
         !sc->hibernation_mode &&
         test_bit(LRUVEC_CONGESTED, &target_lruvec->flags))
         reclaim_throttle(pgdat, VMSCAN_THROTTLE_CONGESTED);
 
     if (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,
                     sc))
         goto again;
 
     /*
      * Kswapd gives up on balancing particular nodes after too
      * many failures to reclaim anything from them and goes to
      * sleep. On reclaim progress, reset the failure counter. A
      * successful direct reclaim run will revive a dormant kswapd.
      */
     if (reclaimable)
         pgdat->kswapd_failures = 0;
 }
 
 /*
  * Returns true if compaction should go ahead for a costly-order request, or
  * the allocation would already succeed without compaction. Return false if we
  * should reclaim first.
  */
 static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
 {
     unsigned long watermark;
     enum compact_result suitable;
 
     suitable = compaction_suitable(zone, sc->order, 0, sc->reclaim_idx);
     if (suitable == COMPACT_SUCCESS)
         /* Allocation should succeed already. Don't reclaim. */
         return true;
     if (suitable == COMPACT_SKIPPED)
         /* Compaction cannot yet proceed. Do reclaim. */
         return false;
 
     /*
      * Compaction is already possible, but it takes time to run and there
      * are potentially other callers using the pages just freed. So proceed
      * with reclaim to make a buffer of free pages available to give
      * compaction a reasonable chance of completing and allocating the page.
      * Note that we won't actually reclaim the whole buffer in one attempt
      * as the target watermark in should_continue_reclaim() is lower. But if
      * we are already above the high+gap watermark, don't reclaim at all.
      */
     watermark = high_wmark_pages(zone) + compact_gap(sc->order);
 
     return zone_watermark_ok_safe(zone, 0, watermark, sc->reclaim_idx);
 }
 
 static void consider_reclaim_throttle(pg_data_t *pgdat, struct scan_control *sc)
 {
     /*
      * If reclaim is making progress greater than 12% efficiency then
      * wake all the NOPROGRESS throttled tasks.
      */
     if (sc->nr_reclaimed > (sc->nr_scanned >> 3)) {
         wait_queue_head_t *wqh;
 
         wqh = &pgdat->reclaim_wait[VMSCAN_THROTTLE_NOPROGRESS];
         if (waitqueue_active(wqh))
             wake_up(wqh);
 
         return;
     }
 
     /*
      * Do not throttle kswapd or cgroup reclaim on NOPROGRESS as it will
      * throttle on VMSCAN_THROTTLE_WRITEBACK if there are too many pages
      * under writeback and marked for immediate reclaim at the tail of the
      * LRU.
      */
     if (current_is_kswapd() || cgroup_reclaim(sc))
         return;
 
     /* Throttle if making no progress at high prioities. */
     if (sc->priority == 1 && !sc->nr_reclaimed)
         reclaim_throttle(pgdat, VMSCAN_THROTTLE_NOPROGRESS);
 }
 
 /*
  * This is the direct reclaim path, for page-allocating processes.  We only
  * try to reclaim pages from zones which will satisfy the caller's allocation
  * request.
  *
  * If a zone is deemed to be full of pinned pages then just give it a light
  * scan then give up on it.
  */
 static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
 {
     struct zoneref *z;
     struct zone *zone;
     unsigned long nr_soft_reclaimed;
     unsigned long nr_soft_scanned;
     gfp_t orig_mask;
     pg_data_t *last_pgdat = NULL;
     pg_data_t *first_pgdat = NULL;
 
     /*
      * If the number of buffer_heads in the machine exceeds the maximum
      * allowed level, force direct reclaim to scan the highmem zone as
      * highmem pages could be pinning lowmem pages storing buffer_heads
      */
     orig_mask = sc->gfp_mask;
     if (buffer_heads_over_limit) {
         sc->gfp_mask |= __GFP_HIGHMEM;
         sc->reclaim_idx = gfp_zone(sc->gfp_mask);
     }
 
     for_each_zone_zonelist_nodemask(zone, z, zonelist,
                     sc->reclaim_idx, sc->nodemask) {
         /*
          * Take care memory controller reclaiming has small influence
          * to global LRU.
          */
         if (!cgroup_reclaim(sc)) {
             if (!cpuset_zone_allowed(zone,
                          GFP_KERNEL | __GFP_HARDWALL))
                 continue;
 
             /*
              * If we already have plenty of memory free for
              * compaction in this zone, don't free any more.
              * Even though compaction is invoked for any
              * non-zero order, only frequent costly order
              * reclamation is disruptive enough to become a
              * noticeable problem, like transparent huge
              * page allocations.
              */
             if (IS_ENABLED(CONFIG_COMPACTION) &&
                 sc->order > PAGE_ALLOC_COSTLY_ORDER &&
                 compaction_ready(zone, sc)) {
                 sc->compaction_ready = true;
                 continue;
             }
 
             /*
              * Shrink each node in the zonelist once. If the
              * zonelist is ordered by zone (not the default) then a
              * node may be shrunk multiple times but in that case
              * the user prefers lower zones being preserved.
              */
             if (zone->zone_pgdat == last_pgdat)
                 continue;
 
             /*
              * This steals pages from memory cgroups over softlimit
              * and returns the number of reclaimed pages and
              * scanned pages. This works for global memory pressure
              * and balancing, not for a memcg's limit.
              */
             nr_soft_scanned = 0;
             nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone->zone_pgdat,
                         sc->order, sc->gfp_mask,
                         &nr_soft_scanned);
             sc->nr_reclaimed += nr_soft_reclaimed;
             sc->nr_scanned += nr_soft_scanned;
             /* need some check for avoid more shrink_zone() */
         }
 
         if (!first_pgdat)
             first_pgdat = zone->zone_pgdat;
 
         /* See comment about same check for global reclaim above */
         if (zone->zone_pgdat == last_pgdat)
             continue;
         last_pgdat = zone->zone_pgdat;
         shrink_node(zone->zone_pgdat, sc);
     }
 
     if (first_pgdat)
         consider_reclaim_throttle(first_pgdat, sc);
 
     /*
      * Restore to original mask to avoid the impact on the caller if we
      * promoted it to __GFP_HIGHMEM.
      */
     sc->gfp_mask = orig_mask;
 }
 
 static void snapshot_refaults(struct mem_cgroup *target_memcg, pg_data_t *pgdat)
 {
     struct lruvec *target_lruvec;
     unsigned long refaults;
 
     target_lruvec = mem_cgroup_lruvec(target_memcg, pgdat);
     refaults = lruvec_page_state(target_lruvec, WORKINGSET_ACTIVATE_ANON);
     target_lruvec->refaults[0] = refaults;
     refaults = lruvec_page_state(target_lruvec, WORKINGSET_ACTIVATE_FILE);
     target_lruvec->refaults[1] = refaults;
 }
 
 /*
  * This is the main entry point to direct page reclaim.
  *
  * If a full scan of the inactive list fails to free enough memory then we
  * are "out of memory" and something needs to be killed.
  *
  * If the caller is !__GFP_FS then the probability of a failure is reasonably
  * high - the zone may be full of dirty or under-writeback pages, which this
  * caller can't do much about.  We kick the writeback threads and take explicit
  * naps in the hope that some of these pages can be written.  But if the
  * allocating task holds filesystem locks which prevent writeout this might not
  * work, and the allocation attempt will fail.
  *
  * returns: 0, if no pages reclaimed
  *      else, the number of pages reclaimed
  */
 static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
                       struct scan_control *sc)
 {
     int initial_priority = sc->priority;
     pg_data_t *last_pgdat;
     struct zoneref *z;
     struct zone *zone;
 retry:
     delayacct_freepages_start();
 
     if (!cgroup_reclaim(sc))
         __count_zid_vm_events(ALLOCSTALL, sc->reclaim_idx, 1);
 
     do {
         if (!sc->proactive)
             vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
                     sc->priority);
         sc->nr_scanned = 0;
         shrink_zones(zonelist, sc);
 
         if (sc->nr_reclaimed >= sc->nr_to_reclaim)
             break;
 
         if (sc->compaction_ready)
             break;
 
         /*
          * If we're getting trouble reclaiming, start doing
          * writepage even in laptop mode.
          */
         if (sc->priority < DEF_PRIORITY - 2)
             sc->may_writepage = 1;
     } while (--sc->priority >= 0);
 
     last_pgdat = NULL;
     for_each_zone_zonelist_nodemask(zone, z, zonelist, sc->reclaim_idx,
                     sc->nodemask) {
         if (zone->zone_pgdat == last_pgdat)
             continue;
         last_pgdat = zone->zone_pgdat;
 
         snapshot_refaults(sc->target_mem_cgroup, zone->zone_pgdat);
 
         if (cgroup_reclaim(sc)) {
             struct lruvec *lruvec;
 
             lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup,
                            zone->zone_pgdat);
             clear_bit(LRUVEC_CONGESTED, &lruvec->flags);
         }
     }
 
     delayacct_freepages_end();
 
     if (sc->nr_reclaimed)
         return sc->nr_reclaimed;
 
     /* Aborted reclaim to try compaction? don't OOM, then */
     if (sc->compaction_ready)
         return 1;
 
     /*
      * We make inactive:active ratio decisions based on the node's
      * composition of memory, but a restrictive reclaim_idx or a
      * memory.low cgroup setting can exempt large amounts of
      * memory from reclaim. Neither of which are very common, so
      * instead of doing costly eligibility calculations of the
      * entire cgroup subtree up front, we assume the estimates are
      * good, and retry with forcible deactivation if that fails.
      */
     if (sc->skipped_deactivate) {
         sc->priority = initial_priority;
         sc->force_deactivate = 1;
         sc->skipped_deactivate = 0;
         goto retry;
     }
 
     /* Untapped cgroup reserves?  Don't OOM, retry. */
     if (sc->memcg_low_skipped) {
         sc->priority = initial_priority;
         sc->force_deactivate = 0;
         sc->memcg_low_reclaim = 1;
         sc->memcg_low_skipped = 0;
         goto retry;
     }
 
     return 0;
 }
 
 static bool allow_direct_reclaim(pg_data_t *pgdat)
 {
     struct zone *zone;
     unsigned long pfmemalloc_reserve = 0;
     unsigned long free_pages = 0;
     int i;
     bool wmark_ok;
 
     if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
         return true;
 
     for (i = 0; i <= ZONE_NORMAL; i++) {
         zone = &pgdat->node_zones[i];
         if (!managed_zone(zone))
             continue;
 
         if (!zone_reclaimable_pages(zone))
             continue;
 
         pfmemalloc_reserve += min_wmark_pages(zone);
         free_pages += zone_page_state(zone, NR_FREE_PAGES);
     }
 
     /* If there are no reserves (unexpected config) then do not throttle */
     if (!pfmemalloc_reserve)
         return true;
 
     wmark_ok = free_pages > pfmemalloc_reserve / 2;
 
     /* kswapd must be awake if processes are being throttled */
     if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
         if (READ_ONCE(pgdat->kswapd_highest_zoneidx) > ZONE_NORMAL)
             WRITE_ONCE(pgdat->kswapd_highest_zoneidx, ZONE_NORMAL);
 
         wake_up_interruptible(&pgdat->kswapd_wait);
     }
 
     return wmark_ok;
 }
 
 /*
  * Throttle direct reclaimers if backing storage is backed by the network
  * and the PFMEMALLOC reserve for the preferred node is getting dangerously
  * depleted. kswapd will continue to make progress and wake the processes
  * when the low watermark is reached.
  *
  * Returns true if a fatal signal was delivered during throttling. If this
  * happens, the page allocator should not consider triggering the OOM killer.
  */
 static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
                     nodemask_t *nodemask)
 {
     struct zoneref *z;
     struct zone *zone;
     pg_data_t *pgdat = NULL;
 
     /*
      * Kernel threads should not be throttled as they may be indirectly
      * responsible for cleaning pages necessary for reclaim to make forward
      * progress. kjournald for example may enter direct reclaim while
      * committing a transaction where throttling it could forcing other
      * processes to block on log_wait_commit().
      */
     if (current->flags & PF_KTHREAD)
         goto out;
 
     /*
      * If a fatal signal is pending, this process should not throttle.
      * It should return quickly so it can exit and free its memory
      */
     if (fatal_signal_pending(current))
         goto out;
 
     /*
      * Check if the pfmemalloc reserves are ok by finding the first node
      * with a usable ZONE_NORMAL or lower zone. The expectation is that
      * GFP_KERNEL will be required for allocating network buffers when
      * swapping over the network so ZONE_HIGHMEM is unusable.
      *
      * Throttling is based on the first usable node and throttled processes
      * wait on a queue until kswapd makes progress and wakes them. There
      * is an affinity then between processes waking up and where reclaim
      * progress has been made assuming the process wakes on the same node.
      * More importantly, processes running on remote nodes will not compete
      * for remote pfmemalloc reserves and processes on different nodes
      * should make reasonable progress.
      */
     for_each_zone_zonelist_nodemask(zone, z, zonelist,
                     gfp_zone(gfp_mask), nodemask) {
         if (zone_idx(zone) > ZONE_NORMAL)
             continue;
 
         /* Throttle based on the first usable node */
         pgdat = zone->zone_pgdat;
         if (allow_direct_reclaim(pgdat))
             goto out;
         break;
     }
 
     /* If no zone was usable by the allocation flags then do not throttle */
     if (!pgdat)
         goto out;
 
     /* Account for the throttling */
     count_vm_event(PGSCAN_DIRECT_THROTTLE);
 
     /*
      * If the caller cannot enter the filesystem, it's possible that it
      * is due to the caller holding an FS lock or performing a journal
      * transaction in the case of a filesystem like ext[3|4]. In this case,
      * it is not safe to block on pfmemalloc_wait as kswapd could be
      * blocked waiting on the same lock. Instead, throttle for up to a
      * second before continuing.
      */
     if (!(gfp_mask & __GFP_FS))
         wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
             allow_direct_reclaim(pgdat), HZ);
     else
         /* Throttle until kswapd wakes the process */
         wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
             allow_direct_reclaim(pgdat));
 
     if (fatal_signal_pending(current))
         return true;
 
 out:
     return false;
 }
 
 unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
                 gfp_t gfp_mask, nodemask_t *nodemask)
 {
     unsigned long nr_reclaimed;
     struct scan_control sc = {
         .nr_to_reclaim = SWAP_CLUSTER_MAX,
         .gfp_mask = current_gfp_context(gfp_mask),
         .reclaim_idx = gfp_zone(gfp_mask),
         .order = order,
         .nodemask = nodemask,
         .priority = DEF_PRIORITY,
         .may_writepage = !laptop_mode,
         .may_unmap = 1,
         .may_swap = 1,
     };
 
     /*
      * scan_control uses s8 fields for order, priority, and reclaim_idx.
      * Confirm they are large enough for max values.
      */
     BUILD_BUG_ON(MAX_ORDER > S8_MAX);
     BUILD_BUG_ON(DEF_PRIORITY > S8_MAX);
     BUILD_BUG_ON(MAX_NR_ZONES > S8_MAX);
 
     /*
      * Do not enter reclaim if fatal signal was delivered while throttled.
      * 1 is returned so that the page allocator does not OOM kill at this
      * point.
      */
     if (throttle_direct_reclaim(sc.gfp_mask, zonelist, nodemask))
         return 1;
 
     set_task_reclaim_state(current, &sc.reclaim_state);
     trace_mm_vmscan_direct_reclaim_begin(order, sc.gfp_mask);
 
     nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
 
     trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
     set_task_reclaim_state(current, NULL);
 
     return nr_reclaimed;
 }
 
 #ifdef CONFIG_MEMCG
 
 /* Only used by soft limit reclaim. Do not reuse for anything else. */
 unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
                         gfp_t gfp_mask, bool noswap,
                         pg_data_t *pgdat,
                         unsigned long *nr_scanned)
 {
     struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
     struct scan_control sc = {
         .nr_to_reclaim = SWAP_CLUSTER_MAX,
         .target_mem_cgroup = memcg,
         .may_writepage = !laptop_mode,
         .may_unmap = 1,
         .reclaim_idx = MAX_NR_ZONES - 1,
         .may_swap = !noswap,
     };
 
     WARN_ON_ONCE(!current->reclaim_state);
 
     sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
             (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
 
     trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
                               sc.gfp_mask);
 
     /*
      * NOTE: Although we can get the priority field, using it
      * here is not a good idea, since it limits the pages we can scan.
      * if we don't reclaim here, the shrink_node from balance_pgdat
      * will pick up pages from other mem cgroup's as well. We hack
      * the priority and make it zero.
      */
     shrink_lruvec(lruvec, &sc);
 
     trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
 
     *nr_scanned = sc.nr_scanned;
 
     return sc.nr_reclaimed;
 }
 
 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
                        unsigned long nr_pages,
                        gfp_t gfp_mask,
                        unsigned int reclaim_options)
 {
     unsigned long nr_reclaimed;
     unsigned int noreclaim_flag;
     struct scan_control sc = {
         .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
         .gfp_mask = (current_gfp_context(gfp_mask) & GFP_RECLAIM_MASK) |
                 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
         .reclaim_idx = MAX_NR_ZONES - 1,
         .target_mem_cgroup = memcg,
         .priority = DEF_PRIORITY,
         .may_writepage = !laptop_mode,
         .may_unmap = 1,
         .may_swap = !!(reclaim_options & MEMCG_RECLAIM_MAY_SWAP),
         .proactive = !!(reclaim_options & MEMCG_RECLAIM_PROACTIVE),
     };
     /*
      * Traverse the ZONELIST_FALLBACK zonelist of the current node to put
      * equal pressure on all the nodes. This is based on the assumption that
      * the reclaim does not bail out early.
      */
     struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
 
     set_task_reclaim_state(current, &sc.reclaim_state);
     trace_mm_vmscan_memcg_reclaim_begin(0, sc.gfp_mask);
     noreclaim_flag = memalloc_noreclaim_save();
 
     nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
 
     memalloc_noreclaim_restore(noreclaim_flag);
     trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
     set_task_reclaim_state(current, NULL);
 
     return nr_reclaimed;
 }
 #endif
 
 static void age_active_anon(struct pglist_data *pgdat,
                 struct scan_control *sc)
 {
     struct mem_cgroup *memcg;
     struct lruvec *lruvec;
 
     if (!can_age_anon_pages(pgdat, sc))
         return;
 
     lruvec = mem_cgroup_lruvec(NULL, pgdat);
     if (!inactive_is_low(lruvec, LRU_INACTIVE_ANON))
         return;
 
     memcg = mem_cgroup_iter(NULL, NULL, NULL);
     do {
         lruvec = mem_cgroup_lruvec(memcg, pgdat);
         shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
                    sc, LRU_ACTIVE_ANON);
         memcg = mem_cgroup_iter(NULL, memcg, NULL);
     } while (memcg);
 }
 
 static bool pgdat_watermark_boosted(pg_data_t *pgdat, int highest_zoneidx)
 {
     int i;
     struct zone *zone;
 
     /*
      * Check for watermark boosts top-down as the higher zones
      * are more likely to be boosted. Both watermarks and boosts
      * should not be checked at the same time as reclaim would
      * start prematurely when there is no boosting and a lower
      * zone is balanced.
      */
     for (i = highest_zoneidx; i >= 0; i--) {
         zone = pgdat->node_zones + i;
         if (!managed_zone(zone))
             continue;
 
         if (zone->watermark_boost)
             return true;
     }
 
     return false;
 }
 
 /*
  * Returns true if there is an eligible zone balanced for the request order
  * and highest_zoneidx
  */
 static bool pgdat_balanced(pg_data_t *pgdat, int order, int highest_zoneidx)
 {
     int i;
     unsigned long mark = -1;
     struct zone *zone;
 
     /*
      * Check watermarks bottom-up as lower zones are more likely to
      * meet watermarks.
      */
     for (i = 0; i <= highest_zoneidx; i++) {
         zone = pgdat->node_zones + i;
 
         if (!managed_zone(zone))
             continue;
 
         if (sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING)
             mark = wmark_pages(zone, WMARK_PROMO);
         else
             mark = high_wmark_pages(zone);
         if (zone_watermark_ok_safe(zone, order, mark, highest_zoneidx))
             return true;
     }
 
     /*
      * If a node has no managed zone within highest_zoneidx, it does not
      * need balancing by definition. This can happen if a zone-restricted
      * allocation tries to wake a remote kswapd.
      */
     if (mark == -1)
         return true;
 
     return false;
 }
 
 /* Clear pgdat state for congested, dirty or under writeback. */
 static void clear_pgdat_congested(pg_data_t *pgdat)
 {
     struct lruvec *lruvec = mem_cgroup_lruvec(NULL, pgdat);
 
     clear_bit(LRUVEC_CONGESTED, &lruvec->flags);
     clear_bit(PGDAT_DIRTY, &pgdat->flags);
     clear_bit(PGDAT_WRITEBACK, &pgdat->flags);
 }
 
 /*
  * Prepare kswapd for sleeping. This verifies that there are no processes
  * waiting in throttle_direct_reclaim() and that watermarks have been met.
  *
  * Returns true if kswapd is ready to sleep
  */
 static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order,
                 int highest_zoneidx)
 {
     /*
      * The throttled processes are normally woken up in balance_pgdat() as
      * soon as allow_direct_reclaim() is true. But there is a potential
      * race between when kswapd checks the watermarks and a process gets
      * throttled. There is also a potential race if processes get
      * throttled, kswapd wakes, a large process exits thereby balancing the
      * zones, which causes kswapd to exit balance_pgdat() before reaching
      * the wake up checks. If kswapd is going to sleep, no process should
      * be sleeping on pfmemalloc_wait, so wake them now if necessary. If
      * the wake up is premature, processes will wake kswapd and get
      * throttled again. The difference from wake ups in balance_pgdat() is
      * that here we are under prepare_to_wait().
      */
     if (waitqueue_active(&pgdat->pfmemalloc_wait))
         wake_up_all(&pgdat->pfmemalloc_wait);
 
     /* Hopeless node, leave it to direct reclaim */
     if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
         return true;
 
     if (pgdat_balanced(pgdat, order, highest_zoneidx)) {
         clear_pgdat_congested(pgdat);
         return true;
     }
 
     return false;
 }
 
 /*
  * kswapd shrinks a node of pages that are at or below the highest usable
  * zone that is currently unbalanced.
  *
  * Returns true if kswapd scanned at least the requested number of pages to
  * reclaim or if the lack of progress was due to pages under writeback.
  * This is used to determine if the scanning priority needs to be raised.
  */
 static bool kswapd_shrink_node(pg_data_t *pgdat,
                    struct scan_control *sc)
 {
     struct zone *zone;
     int z;
 
     /* Reclaim a number of pages proportional to the number of zones */
     sc->nr_to_reclaim = 0;
     for (z = 0; z <= sc->reclaim_idx; z++) {
         zone = pgdat->node_zones + z;
         if (!managed_zone(zone))
             continue;
 
         sc->nr_to_reclaim += max(high_wmark_pages(zone), SWAP_CLUSTER_MAX);
     }
 
     /*
      * Historically care was taken to put equal pressure on all zones but
      * now pressure is applied based on node LRU order.
      */
     shrink_node(pgdat, sc);
 
     /*
      * Fragmentation may mean that the system cannot be rebalanced for
      * high-order allocations. If twice the allocation size has been
      * reclaimed then recheck watermarks only at order-0 to prevent
      * excessive reclaim. Assume that a process requested a high-order
      * can direct reclaim/compact.
      */
     if (sc->order && sc->nr_reclaimed >= compact_gap(sc->order))
         sc->order = 0;
 
     return sc->nr_scanned >= sc->nr_to_reclaim;
 }
 
 /* Page allocator PCP high watermark is lowered if reclaim is active. */
 static inline void
 update_reclaim_active(pg_data_t *pgdat, int highest_zoneidx, bool active)
 {
     int i;
     struct zone *zone;
 
     for (i = 0; i <= highest_zoneidx; i++) {
         zone = pgdat->node_zones + i;
 
         if (!managed_zone(zone))
             continue;
 
         if (active)
             set_bit(ZONE_RECLAIM_ACTIVE, &zone->flags);
         else
             clear_bit(ZONE_RECLAIM_ACTIVE, &zone->flags);
     }
 }
 
 static inline void
 set_reclaim_active(pg_data_t *pgdat, int highest_zoneidx)
 {
     update_reclaim_active(pgdat, highest_zoneidx, true);
 }
 
 static inline void
 clear_reclaim_active(pg_data_t *pgdat, int highest_zoneidx)
 {
     update_reclaim_active(pgdat, highest_zoneidx, false);
 }
 
 /*
  * For kswapd, balance_pgdat() will reclaim pages across a node from zones
  * that are eligible for use by the caller until at least one zone is
  * balanced.
  *
  * Returns the order kswapd finished reclaiming at.
  *
  * kswapd scans the zones in the highmem->normal->dma direction.  It skips
  * zones which have free_pages > high_wmark_pages(zone), but once a zone is
  * found to have free_pages <= high_wmark_pages(zone), any page in that zone
  * or lower is eligible for reclaim until at least one usable zone is
  * balanced.
  */
 static int balance_pgdat(pg_data_t *pgdat, int order, int highest_zoneidx)
 {
     int i;
     unsigned long nr_soft_reclaimed;
     unsigned long nr_soft_scanned;
     unsigned long pflags;
     unsigned long nr_boost_reclaim;
     unsigned long zone_boosts[MAX_NR_ZONES] = { 0, };
     bool boosted;
     struct zone *zone;
     struct scan_control sc = {
         .gfp_mask = GFP_KERNEL,
         .order = order,
         .may_unmap = 1,
     };
 
     set_task_reclaim_state(current, &sc.reclaim_state);
     psi_memstall_enter(&pflags);
     __fs_reclaim_acquire(_THIS_IP_);
 
     count_vm_event(PAGEOUTRUN);
 
     /*
      * Account for the reclaim boost. Note that the zone boost is left in
      * place so that parallel allocations that are near the watermark will
      * stall or direct reclaim until kswapd is finished.
      */
     nr_boost_reclaim = 0;
     for (i = 0; i <= highest_zoneidx; i++) {
         zone = pgdat->node_zones + i;
         if (!managed_zone(zone))
             continue;
 
         nr_boost_reclaim += zone->watermark_boost;
         zone_boosts[i] = zone->watermark_boost;
     }
     boosted = nr_boost_reclaim;
 
 restart:
     set_reclaim_active(pgdat, highest_zoneidx);
     sc.priority = DEF_PRIORITY;
     do {
         unsigned long nr_reclaimed = sc.nr_reclaimed;
         bool raise_priority = true;
         bool balanced;
         bool ret;
 
         sc.reclaim_idx = highest_zoneidx;
 
         /*
          * If the number of buffer_heads exceeds the maximum allowed
          * then consider reclaiming from all zones. This has a dual
          * purpose -- on 64-bit systems it is expected that
          * buffer_heads are stripped during active rotation. On 32-bit
          * systems, highmem pages can pin lowmem memory and shrinking
          * buffers can relieve lowmem pressure. Reclaim may still not
          * go ahead if all eligible zones for the original allocation
          * request are balanced to avoid excessive reclaim from kswapd.
          */
         if (buffer_heads_over_limit) {
             for (i = MAX_NR_ZONES - 1; i >= 0; i--) {
                 zone = pgdat->node_zones + i;
                 if (!managed_zone(zone))
                     continue;
 
                 sc.reclaim_idx = i;
                 break;
             }
         }
 
         /*
          * If the pgdat is imbalanced then ignore boosting and preserve
          * the watermarks for a later time and restart. Note that the
          * zone watermarks will be still reset at the end of balancing
          * on the grounds that the normal reclaim should be enough to
          * re-evaluate if boosting is required when kswapd next wakes.
          */
         balanced = pgdat_balanced(pgdat, sc.order, highest_zoneidx);
         if (!balanced && nr_boost_reclaim) {
             nr_boost_reclaim = 0;
             goto restart;
         }
 
         /*
          * If boosting is not active then only reclaim if there are no
          * eligible zones. Note that sc.reclaim_idx is not used as
          * buffer_heads_over_limit may have adjusted it.
          */
         if (!nr_boost_reclaim && balanced)
             goto out;
 
         /* Limit the priority of boosting to avoid reclaim writeback */
         if (nr_boost_reclaim && sc.priority == DEF_PRIORITY - 2)
             raise_priority = false;
 
         /*
          * Do not writeback or swap pages for boosted reclaim. The
          * intent is to relieve pressure not issue sub-optimal IO
          * from reclaim context. If no pages are reclaimed, the
          * reclaim will be aborted.
          */
         sc.may_writepage = !laptop_mode && !nr_boost_reclaim;
         sc.may_swap = !nr_boost_reclaim;
 
         /*
          * Do some background aging of the anon list, to give
          * pages a chance to be referenced before reclaiming. All
          * pages are rotated regardless of classzone as this is
          * about consistent aging.
          */
         age_active_anon(pgdat, &sc);
 
         /*
          * If we're getting trouble reclaiming, start doing writepage
          * even in laptop mode.
          */
         if (sc.priority < DEF_PRIORITY - 2)
             sc.may_writepage = 1;
 
         /* Call soft limit reclaim before calling shrink_node. */
         sc.nr_scanned = 0;
         nr_soft_scanned = 0;
         nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(pgdat, sc.order,
                         sc.gfp_mask, &nr_soft_scanned);
         sc.nr_reclaimed += nr_soft_reclaimed;
 
         /*
          * There should be no need to raise the scanning priority if
          * enough pages are already being scanned that that high
          * watermark would be met at 100% efficiency.
          */
         if (kswapd_shrink_node(pgdat, &sc))
             raise_priority = false;
 
         /*
          * If the low watermark is met there is no need for processes
          * to be throttled on pfmemalloc_wait as they should not be
          * able to safely make forward progress. Wake them
          */
         if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
                 allow_direct_reclaim(pgdat))
             wake_up_all(&pgdat->pfmemalloc_wait);
 
         /* Check if kswapd should be suspending */
         __fs_reclaim_release(_THIS_IP_);
         ret = try_to_freeze();
         __fs_reclaim_acquire(_THIS_IP_);
         if (ret || kthread_should_stop())
             break;
 
         /*
          * Raise priority if scanning rate is too low or there was no
          * progress in reclaiming pages
          */
         nr_reclaimed = sc.nr_reclaimed - nr_reclaimed;
         nr_boost_reclaim -= min(nr_boost_reclaim, nr_reclaimed);
 
         /*
          * If reclaim made no progress for a boost, stop reclaim as
          * IO cannot be queued and it could be an infinite loop in
          * extreme circumstances.
          */
         if (nr_boost_reclaim && !nr_reclaimed)
             break;
 
         if (raise_priority || !nr_reclaimed)
             sc.priority--;
     } while (sc.priority >= 1);
 
     if (!sc.nr_reclaimed)
         pgdat->kswapd_failures++;
 
 out:
     clear_reclaim_active(pgdat, highest_zoneidx);
 
     /* If reclaim was boosted, account for the reclaim done in this pass */
     if (boosted) {
         unsigned long flags;
 
         for (i = 0; i <= highest_zoneidx; i++) {
             if (!zone_boosts[i])
                 continue;
 
             /* Increments are under the zone lock */
             zone = pgdat->node_zones + i;
             spin_lock_irqsave(&zone->lock, flags);
             zone->watermark_boost -= min(zone->watermark_boost, zone_boosts[i]);
             spin_unlock_irqrestore(&zone->lock, flags);
         }
 
         /*
          * As there is now likely space, wakeup kcompact to defragment
          * pageblocks.
          */
         wakeup_kcompactd(pgdat, pageblock_order, highest_zoneidx);
     }
 
     snapshot_refaults(NULL, pgdat);
     __fs_reclaim_release(_THIS_IP_);
     psi_memstall_leave(&pflags);
     set_task_reclaim_state(current, NULL);
 
     /*
      * Return the order kswapd stopped reclaiming at as
      * prepare_kswapd_sleep() takes it into account. If another caller
      * entered the allocator slow path while kswapd was awake, order will
      * remain at the higher level.
      */
     return sc.order;
 }
 
 /*
  * The pgdat->kswapd_highest_zoneidx is used to pass the highest zone index to
  * be reclaimed by kswapd from the waker. If the value is MAX_NR_ZONES which is
  * not a valid index then either kswapd runs for first time or kswapd couldn't
  * sleep after previous reclaim attempt (node is still unbalanced). In that
  * case return the zone index of the previous kswapd reclaim cycle.
  */
 static enum zone_type kswapd_highest_zoneidx(pg_data_t *pgdat,
                        enum zone_type prev_highest_zoneidx)
 {
     enum zone_type curr_idx = READ_ONCE(pgdat->kswapd_highest_zoneidx);
 
     return curr_idx == MAX_NR_ZONES ? prev_highest_zoneidx : curr_idx;
 }
 
 static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_order,
                 unsigned int highest_zoneidx)
 {
     long remaining = 0;
     DEFINE_WAIT(wait);
 
     if (freezing(current) || kthread_should_stop())
         return;
 
     prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
 
     /*
      * Try to sleep for a short interval. Note that kcompactd will only be
      * woken if it is possible to sleep for a short interval. This is
      * deliberate on the assumption that if reclaim cannot keep an
      * eligible zone balanced that it's also unlikely that compaction will
      * succeed.
      */
     if (prepare_kswapd_sleep(pgdat, reclaim_order, highest_zoneidx)) {
         /*
          * Compaction records what page blocks it recently failed to
          * isolate pages from and skips them in the future scanning.
          * When kswapd is going to sleep, it is reasonable to assume
          * that pages and compaction may succeed so reset the cache.
          */
         reset_isolation_suitable(pgdat);
 
         /*
          * We have freed the memory, now we should compact it to make
          * allocation of the requested order possible.
          */
         wakeup_kcompactd(pgdat, alloc_order, highest_zoneidx);
 
         remaining = schedule_timeout(HZ/10);
 
         /*
          * If woken prematurely then reset kswapd_highest_zoneidx and
          * order. The values will either be from a wakeup request or
          * the previous request that slept prematurely.
          */
         if (remaining) {
             WRITE_ONCE(pgdat->kswapd_highest_zoneidx,
                     kswapd_highest_zoneidx(pgdat,
                             highest_zoneidx));
 
             if (READ_ONCE(pgdat->kswapd_order) < reclaim_order)
                 WRITE_ONCE(pgdat->kswapd_order, reclaim_order);
         }
 
         finish_wait(&pgdat->kswapd_wait, &wait);
         prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
     }
 
     /*
      * After a short sleep, check if it was a premature sleep. If not, then
      * go fully to sleep until explicitly woken up.
      */
     if (!remaining &&
         prepare_kswapd_sleep(pgdat, reclaim_order, highest_zoneidx)) {
         trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
 
         /*
          * vmstat counters are not perfectly accurate and the estimated
          * value for counters such as NR_FREE_PAGES can deviate from the
          * true value by nr_online_cpus * threshold. To avoid the zone
          * watermarks being breached while under pressure, we reduce the
          * per-cpu vmstat threshold while kswapd is awake and restore
          * them before going back to sleep.
          */
         set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
 
         if (!kthread_should_stop())
             schedule();
 
         set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
     } else {
         if (remaining)
             count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
         else
             count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
     }
     finish_wait(&pgdat->kswapd_wait, &wait);
 }
 
 /*
  * The background pageout daemon, started as a kernel thread
  * from the init process.
  *
  * This basically trickles out pages so that we have _some_
  * free memory available even if there is no other activity
  * that frees anything up. This is needed for things like routing
  * etc, where we otherwise might have all activity going on in
  * asynchronous contexts that cannot page things out.
  *
  * If there are applications that are active memory-allocators
  * (most normal use), this basically shouldn't matter.
  */
 static int kswapd(void *p)
 {
     unsigned int alloc_order, reclaim_order;
     unsigned int highest_zoneidx = MAX_NR_ZONES - 1;
     pg_data_t *pgdat = (pg_data_t *)p;
     struct task_struct *tsk = current;
     const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
 
     if (!cpumask_empty(cpumask))
         set_cpus_allowed_ptr(tsk, cpumask);
 
     /*
      * Tell the memory management that we're a "memory allocator",
      * and that if we need more memory we should get access to it
      * regardless (see "__alloc_pages()"). "kswapd" should
      * never get caught in the normal page freeing logic.
      *
      * (Kswapd normally doesn't need memory anyway, but sometimes
      * you need a small amount of memory in order to be able to
      * page out something else, and this flag essentially protects
      * us from recursively trying to free more memory as we're
      * trying to free the first piece of memory in the first place).
      */
     tsk->flags |= PF_MEMALLOC | PF_KSWAPD;
     set_freezable();
 
     WRITE_ONCE(pgdat->kswapd_order, 0);
     WRITE_ONCE(pgdat->kswapd_highest_zoneidx, MAX_NR_ZONES);
     atomic_set(&pgdat->nr_writeback_throttled, 0);
     for ( ; ; ) {
         bool ret;
 
         alloc_order = reclaim_order = READ_ONCE(pgdat->kswapd_order);
         highest_zoneidx = kswapd_highest_zoneidx(pgdat,
                             highest_zoneidx);
 
 kswapd_try_sleep:
         kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order,
                     highest_zoneidx);
 
         /* Read the new order and highest_zoneidx */
         alloc_order = READ_ONCE(pgdat->kswapd_order);
         highest_zoneidx = kswapd_highest_zoneidx(pgdat,
                             highest_zoneidx);
         WRITE_ONCE(pgdat->kswapd_order, 0);
         WRITE_ONCE(pgdat->kswapd_highest_zoneidx, MAX_NR_ZONES);
 
         ret = try_to_freeze();
         if (kthread_should_stop())
             break;
 
         /*
          * We can speed up thawing tasks if we don't call balance_pgdat
          * after returning from the refrigerator
          */
         if (ret)
             continue;
 
         /*
          * Reclaim begins at the requested order but if a high-order
          * reclaim fails then kswapd falls back to reclaiming for
          * order-0. If that happens, kswapd will consider sleeping
          * for the order it finished reclaiming at (reclaim_order)
          * but kcompactd is woken to compact for the original
          * request (alloc_order).
          */
         trace_mm_vmscan_kswapd_wake(pgdat->node_id, highest_zoneidx,
                         alloc_order);
         reclaim_order = balance_pgdat(pgdat, alloc_order,
                         highest_zoneidx);
         if (reclaim_order < alloc_order)
             goto kswapd_try_sleep;
     }
 
     tsk->flags &= ~(PF_MEMALLOC | PF_KSWAPD);
 
     return 0;
 }
 
 /*
  * A zone is low on free memory or too fragmented for high-order memory.  If
  * kswapd should reclaim (direct reclaim is deferred), wake it up for the zone's
  * pgdat.  It will wake up kcompactd after reclaiming memory.  If kswapd reclaim
  * has failed or is not needed, still wake up kcompactd if only compaction is
  * needed.
  */
 void wakeup_kswapd(struct zone *zone, gfp_t gfp_flags, int order,
            enum zone_type highest_zoneidx)
 {
     pg_data_t *pgdat;
     enum zone_type curr_idx;
 
     if (!managed_zone(zone))
         return;
 
     if (!cpuset_zone_allowed(zone, gfp_flags))
         return;
 
     pgdat = zone->zone_pgdat;
     curr_idx = READ_ONCE(pgdat->kswapd_highest_zoneidx);
 
     if (curr_idx == MAX_NR_ZONES || curr_idx < highest_zoneidx)
         WRITE_ONCE(pgdat->kswapd_highest_zoneidx, highest_zoneidx);
 
     if (READ_ONCE(pgdat->kswapd_order) < order)
         WRITE_ONCE(pgdat->kswapd_order, order);
 
     if (!waitqueue_active(&pgdat->kswapd_wait))
         return;
 
     /* Hopeless node, leave it to direct reclaim if possible */
     if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES ||
         (pgdat_balanced(pgdat, order, highest_zoneidx) &&
          !pgdat_watermark_boosted(pgdat, highest_zoneidx))) {
         /*
          * There may be plenty of free memory available, but it's too
          * fragmented for high-order allocations.  Wake up kcompactd
          * and rely on compaction_suitable() to determine if it's
          * needed.  If it fails, it will defer subsequent attempts to
          * ratelimit its work.
          */
         if (!(gfp_flags & __GFP_DIRECT_RECLAIM))
             wakeup_kcompactd(pgdat, order, highest_zoneidx);
         return;
     }
 
     trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, highest_zoneidx, order,
                       gfp_flags);
     wake_up_interruptible(&pgdat->kswapd_wait);
 }
 
 #ifdef CONFIG_HIBERNATION
 /*
  * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
  * freed pages.
  *
  * Rather than trying to age LRUs the aim is to preserve the overall
  * LRU order by reclaiming preferentially
  * inactive > active > active referenced > active mapped
  */
 unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
 {
     struct scan_control sc = {
         .nr_to_reclaim = nr_to_reclaim,
         .gfp_mask = GFP_HIGHUSER_MOVABLE,
         .reclaim_idx = MAX_NR_ZONES - 1,
         .priority = DEF_PRIORITY,
         .may_writepage = 1,
         .may_unmap = 1,
         .may_swap = 1,
         .hibernation_mode = 1,
     };
     struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
     unsigned long nr_reclaimed;
     unsigned int noreclaim_flag;
 
     fs_reclaim_acquire(sc.gfp_mask);
     noreclaim_flag = memalloc_noreclaim_save();
     set_task_reclaim_state(current, &sc.reclaim_state);
 
     nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
 
     set_task_reclaim_state(current, NULL);
     memalloc_noreclaim_restore(noreclaim_flag);
     fs_reclaim_release(sc.gfp_mask);
 
     return nr_reclaimed;
 }
 #endif /* CONFIG_HIBERNATION */
 
 /*
  * This kswapd start function will be called by init and node-hot-add.
  */
 void kswapd_run(int nid)
 {
     pg_data_t *pgdat = NODE_DATA(nid);
 
     if (pgdat->kswapd)
         return;
 
     pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
     if (IS_ERR(pgdat->kswapd)) {
         /* failure at boot is fatal */
         BUG_ON(system_state < SYSTEM_RUNNING);
         pr_err("Failed to start kswapd on node %d\n", nid);
         pgdat->kswapd = NULL;
     }
 }
 
 /*
  * Called by memory hotplug when all memory in a node is offlined.  Caller must
  * be holding mem_hotplug_begin/done().
  */
 void kswapd_stop(int nid)
 {
     struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
 
     if (kswapd) {
         kthread_stop(kswapd);
         NODE_DATA(nid)->kswapd = NULL;
     }
 }
 
 static int __init kswapd_init(void)
 {
     int nid;
 
     swap_setup();
     for_each_node_state(nid, N_MEMORY)
         kswapd_run(nid);
     return 0;
 }
 
 module_init(kswapd_init)
 
 #ifdef CONFIG_NUMA
 /*
  * Node reclaim mode
  *
  * If non-zero call node_reclaim when the number of free pages falls below
  * the watermarks.
  */
 int node_reclaim_mode __read_mostly;
 
 /*
  * Priority for NODE_RECLAIM. This determines the fraction of pages
  * of a node considered for each zone_reclaim. 4 scans 1/16th of
  * a zone.
  */
 #define NODE_RECLAIM_PRIORITY 4
 
 /*
  * Percentage of pages in a zone that must be unmapped for node_reclaim to
  * occur.
  */
 int sysctl_min_unmapped_ratio = 1;
 
 /*
  * If the number of slab pages in a zone grows beyond this percentage then
  * slab reclaim needs to occur.
  */
 int sysctl_min_slab_ratio = 5;
 
 static inline unsigned long node_unmapped_file_pages(struct pglist_data *pgdat)
 {
     unsigned long file_mapped = node_page_state(pgdat, NR_FILE_MAPPED);
     unsigned long file_lru = node_page_state(pgdat, NR_INACTIVE_FILE) +
         node_page_state(pgdat, NR_ACTIVE_FILE);
 
     /*
      * It's possible for there to be more file mapped pages than
      * accounted for by the pages on the file LRU lists because
      * tmpfs pages accounted for as ANON can also be FILE_MAPPED
      */
     return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
 }
 
 /* Work out how many page cache pages we can reclaim in this reclaim_mode */
 static unsigned long node_pagecache_reclaimable(struct pglist_data *pgdat)
 {
     unsigned long nr_pagecache_reclaimable;
     unsigned long delta = 0;
 
     /*
      * If RECLAIM_UNMAP is set, then all file pages are considered
      * potentially reclaimable. Otherwise, we have to worry about
      * pages like swapcache and node_unmapped_file_pages() provides
      * a better estimate
      */
     if (node_reclaim_mode & RECLAIM_UNMAP)
         nr_pagecache_reclaimable = node_page_state(pgdat, NR_FILE_PAGES);
     else
         nr_pagecache_reclaimable = node_unmapped_file_pages(pgdat);
 
     /* If we can't clean pages, remove dirty pages from consideration */
     if (!(node_reclaim_mode & RECLAIM_WRITE))
         delta += node_page_state(pgdat, NR_FILE_DIRTY);
 
     /* Watch for any possible underflows due to delta */
     if (unlikely(delta > nr_pagecache_reclaimable))
         delta = nr_pagecache_reclaimable;
 
     return nr_pagecache_reclaimable - delta;
 }
 
 /*
  * Try to free up some pages from this node through reclaim.
  */
 static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
 {
     /* Minimum pages needed in order to stay on node */
     const unsigned long nr_pages = 1 << order;
     struct task_struct *p = current;
     unsigned int noreclaim_flag;
     struct scan_control sc = {
         .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
         .gfp_mask = current_gfp_context(gfp_mask),
         .order = order,
         .priority = NODE_RECLAIM_PRIORITY,
         .may_writepage = !!(node_reclaim_mode & RECLAIM_WRITE),
         .may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP),
         .may_swap = 1,
         .reclaim_idx = gfp_zone(gfp_mask),
     };
     unsigned long pflags;
 
     trace_mm_vmscan_node_reclaim_begin(pgdat->node_id, order,
                        sc.gfp_mask);
 
     cond_resched();
     psi_memstall_enter(&pflags);
     fs_reclaim_acquire(sc.gfp_mask);
     /*
      * We need to be able to allocate from the reserves for RECLAIM_UNMAP
      */
     noreclaim_flag = memalloc_noreclaim_save();
     set_task_reclaim_state(p, &sc.reclaim_state);
 
     if (node_pagecache_reclaimable(pgdat) > pgdat->min_unmapped_pages ||
         node_page_state_pages(pgdat, NR_SLAB_RECLAIMABLE_B) > pgdat->min_slab_pages) {
         /*
          * Free memory by calling shrink node with increasing
          * priorities until we have enough memory freed.
          */
         do {
             shrink_node(pgdat, &sc);
         } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
     }
 
     set_task_reclaim_state(p, NULL);
     memalloc_noreclaim_restore(noreclaim_flag);
     fs_reclaim_release(sc.gfp_mask);
     psi_memstall_leave(&pflags);
 
     trace_mm_vmscan_node_reclaim_end(sc.nr_reclaimed);
 
     return sc.nr_reclaimed >= nr_pages;
 }
 
 int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
 {
     int ret;
 
     /*
      * Node reclaim reclaims unmapped file backed pages and
      * slab pages if we are over the defined limits.
      *
      * A small portion of unmapped file backed pages is needed for
      * file I/O otherwise pages read by file I/O will be immediately
      * thrown out if the node is overallocated. So we do not reclaim
      * if less than a specified percentage of the node is used by
      * unmapped file backed pages.
      */
     if (node_pagecache_reclaimable(pgdat) <= pgdat->min_unmapped_pages &&
         node_page_state_pages(pgdat, NR_SLAB_RECLAIMABLE_B) <=
         pgdat->min_slab_pages)
         return NODE_RECLAIM_FULL;
 
     /*
      * Do not scan if the allocation should not be delayed.
      */
     if (!gfpflags_allow_blocking(gfp_mask) || (current->flags & PF_MEMALLOC))
         return NODE_RECLAIM_NOSCAN;
 
     /*
      * Only run node reclaim on the local node or on nodes that do not
      * have associated processors. This will favor the local processor
      * over remote processors and spread off node memory allocations
      * as wide as possible.
      */
     if (node_state(pgdat->node_id, N_CPU) && pgdat->node_id != numa_node_id())
         return NODE_RECLAIM_NOSCAN;
 
     if (test_and_set_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags))
         return NODE_RECLAIM_NOSCAN;
 
     ret = __node_reclaim(pgdat, gfp_mask, order);
     clear_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags);
 
     if (!ret)
         count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
 
     return ret;
 }
 #endif
 
 void check_move_unevictable_pages(struct pagevec *pvec)
 {
     struct folio_batch fbatch;
     unsigned i;
 
     folio_batch_init(&fbatch);
     for (i = 0; i < pvec->nr; i++) {
         struct page *page = pvec->pages[i];
 
         if (PageTransTail(page))
             continue;
         folio_batch_add(&fbatch, page_folio(page));
     }
     check_move_unevictable_folios(&fbatch);
 }
 EXPORT_SYMBOL_GPL(check_move_unevictable_pages);
 
 /**
  * check_move_unevictable_folios - Move evictable folios to appropriate zone
  * lru list
  * @fbatch: Batch of lru folios to check.
  *
  * Checks folios for evictability, if an evictable folio is in the unevictable
  * lru list, moves it to the appropriate evictable lru list. This function
  * should be only used for lru folios.
  */
 void check_move_unevictable_folios(struct folio_batch *fbatch)
 {
     struct lruvec *lruvec = NULL;
     int pgscanned = 0;
     int pgrescued = 0;
     int i;
 
     for (i = 0; i < fbatch->nr; i++) {
         struct folio *folio = fbatch->folios[i];
         int nr_pages = folio_nr_pages(folio);
 
         pgscanned += nr_pages;
 
         /* block memcg migration while the folio moves between lrus */
         if (!folio_test_clear_lru(folio))
             continue;
 
         lruvec = folio_lruvec_relock_irq(folio, lruvec);
         if (folio_evictable(folio) && folio_test_unevictable(folio)) {
             lruvec_del_folio(lruvec, folio);
             folio_clear_unevictable(folio);
             lruvec_add_folio(lruvec, folio);
             pgrescued += nr_pages;
         }
         folio_set_lru(folio);
     }
 
     if (lruvec) {
         __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
         __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
         unlock_page_lruvec_irq(lruvec);
     } else if (pgscanned) {
         count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
     }
 }
 EXPORT_SYMBOL_GPL(check_move_unevictable_folios);