OSCL-LXR linux-6.0.1/​mm/​swapfile.c	Source navigation Diff markup Identifier search General search
	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-only
 /*
  *  linux/mm/swapfile.c
  *
  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  *  Swap reorganised 29.12.95, Stephen Tweedie
  */
 
 #include <linux/blkdev.h>
 #include <linux/mm.h>
 #include <linux/sched/mm.h>
 #include <linux/sched/task.h>
 #include <linux/hugetlb.h>
 #include <linux/mman.h>
 #include <linux/slab.h>
 #include <linux/kernel_stat.h>
 #include <linux/swap.h>
 #include <linux/vmalloc.h>
 #include <linux/pagemap.h>
 #include <linux/namei.h>
 #include <linux/shmem_fs.h>
 #include <linux/blk-cgroup.h>
 #include <linux/random.h>
 #include <linux/writeback.h>
 #include <linux/proc_fs.h>
 #include <linux/seq_file.h>
 #include <linux/init.h>
 #include <linux/ksm.h>
 #include <linux/rmap.h>
 #include <linux/security.h>
 #include <linux/backing-dev.h>
 #include <linux/mutex.h>
 #include <linux/capability.h>
 #include <linux/syscalls.h>
 #include <linux/memcontrol.h>
 #include <linux/poll.h>
 #include <linux/oom.h>
 #include <linux/frontswap.h>
 #include <linux/swapfile.h>
 #include <linux/export.h>
 #include <linux/swap_slots.h>
 #include <linux/sort.h>
 #include <linux/completion.h>
 
 #include <asm/tlbflush.h>
 #include <linux/swapops.h>
 #include <linux/swap_cgroup.h>
 #include "swap.h"
 
 static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
                  unsigned char);
 static void free_swap_count_continuations(struct swap_info_struct *);
 
 static DEFINE_SPINLOCK(swap_lock);
 static unsigned int nr_swapfiles;
 atomic_long_t nr_swap_pages;
 /*
  * Some modules use swappable objects and may try to swap them out under
  * memory pressure (via the shrinker). Before doing so, they may wish to
  * check to see if any swap space is available.
  */
 EXPORT_SYMBOL_GPL(nr_swap_pages);
 /* protected with swap_lock. reading in vm_swap_full() doesn't need lock */
 long total_swap_pages;
 static int least_priority = -1;
 
 static const char Bad_file[] = "Bad swap file entry ";
 static const char Unused_file[] = "Unused swap file entry ";
 static const char Bad_offset[] = "Bad swap offset entry ";
 static const char Unused_offset[] = "Unused swap offset entry ";
 
 /*
  * all active swap_info_structs
  * protected with swap_lock, and ordered by priority.
  */
 static PLIST_HEAD(swap_active_head);
 
 /*
  * all available (active, not full) swap_info_structs
  * protected with swap_avail_lock, ordered by priority.
  * This is used by folio_alloc_swap() instead of swap_active_head
  * because swap_active_head includes all swap_info_structs,
  * but folio_alloc_swap() doesn't need to look at full ones.
  * This uses its own lock instead of swap_lock because when a
  * swap_info_struct changes between not-full/full, it needs to
  * add/remove itself to/from this list, but the swap_info_struct->lock
  * is held and the locking order requires swap_lock to be taken
  * before any swap_info_struct->lock.
  */
 static struct plist_head *swap_avail_heads;
 static DEFINE_SPINLOCK(swap_avail_lock);
 
 struct swap_info_struct *swap_info[MAX_SWAPFILES];
 
 static DEFINE_MUTEX(swapon_mutex);
 
 static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait);
 /* Activity counter to indicate that a swapon or swapoff has occurred */
 static atomic_t proc_poll_event = ATOMIC_INIT(0);
 
 atomic_t nr_rotate_swap = ATOMIC_INIT(0);
 
 static struct swap_info_struct *swap_type_to_swap_info(int type)
 {
     if (type >= MAX_SWAPFILES)
         return NULL;
 
     return READ_ONCE(swap_info[type]); /* rcu_dereference() */
 }
 
 static inline unsigned char swap_count(unsigned char ent)
 {
     return ent & ~SWAP_HAS_CACHE;   /* may include COUNT_CONTINUED flag */
 }
 
 /* Reclaim the swap entry anyway if possible */
 #define TTRS_ANYWAY     0x1
 /*
  * Reclaim the swap entry if there are no more mappings of the
  * corresponding page
  */
 #define TTRS_UNMAPPED       0x2
 /* Reclaim the swap entry if swap is getting full*/
 #define TTRS_FULL       0x4
 
 /* returns 1 if swap entry is freed */
 static int __try_to_reclaim_swap(struct swap_info_struct *si,
                  unsigned long offset, unsigned long flags)
 {
     swp_entry_t entry = swp_entry(si->type, offset);
     struct page *page;
     int ret = 0;
 
     page = find_get_page(swap_address_space(entry), offset);
     if (!page)
         return 0;
     /*
      * When this function is called from scan_swap_map_slots() and it's
      * called by vmscan.c at reclaiming pages. So, we hold a lock on a page,
      * here. We have to use trylock for avoiding deadlock. This is a special
      * case and you should use try_to_free_swap() with explicit lock_page()
      * in usual operations.
      */
     if (trylock_page(page)) {
         if ((flags & TTRS_ANYWAY) ||
             ((flags & TTRS_UNMAPPED) && !page_mapped(page)) ||
             ((flags & TTRS_FULL) && mem_cgroup_swap_full(page)))
             ret = try_to_free_swap(page);
         unlock_page(page);
     }
     put_page(page);
     return ret;
 }
 
 static inline struct swap_extent *first_se(struct swap_info_struct *sis)
 {
     struct rb_node *rb = rb_first(&sis->swap_extent_root);
     return rb_entry(rb, struct swap_extent, rb_node);
 }
 
 static inline struct swap_extent *next_se(struct swap_extent *se)
 {
     struct rb_node *rb = rb_next(&se->rb_node);
     return rb ? rb_entry(rb, struct swap_extent, rb_node) : NULL;
 }
 
 /*
  * swapon tell device that all the old swap contents can be discarded,
  * to allow the swap device to optimize its wear-levelling.
  */
 static int discard_swap(struct swap_info_struct *si)
 {
     struct swap_extent *se;
     sector_t start_block;
     sector_t nr_blocks;
     int err = 0;
 
     /* Do not discard the swap header page! */
     se = first_se(si);
     start_block = (se->start_block + 1) << (PAGE_SHIFT - 9);
     nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
     if (nr_blocks) {
         err = blkdev_issue_discard(si->bdev, start_block,
                 nr_blocks, GFP_KERNEL);
         if (err)
             return err;
         cond_resched();
     }
 
     for (se = next_se(se); se; se = next_se(se)) {
         start_block = se->start_block << (PAGE_SHIFT - 9);
         nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
 
         err = blkdev_issue_discard(si->bdev, start_block,
                 nr_blocks, GFP_KERNEL);
         if (err)
             break;
 
         cond_resched();
     }
     return err;     /* That will often be -EOPNOTSUPP */
 }
 
 static struct swap_extent *
 offset_to_swap_extent(struct swap_info_struct *sis, unsigned long offset)
 {
     struct swap_extent *se;
     struct rb_node *rb;
 
     rb = sis->swap_extent_root.rb_node;
     while (rb) {
         se = rb_entry(rb, struct swap_extent, rb_node);
         if (offset < se->start_page)
             rb = rb->rb_left;
         else if (offset >= se->start_page + se->nr_pages)
             rb = rb->rb_right;
         else
             return se;
     }
     /* It *must* be present */
     BUG();
 }
 
 sector_t swap_page_sector(struct page *page)
 {
     struct swap_info_struct *sis = page_swap_info(page);
     struct swap_extent *se;
     sector_t sector;
     pgoff_t offset;
 
     offset = __page_file_index(page);
     se = offset_to_swap_extent(sis, offset);
     sector = se->start_block + (offset - se->start_page);
     return sector << (PAGE_SHIFT - 9);
 }
 
 /*
  * swap allocation tell device that a cluster of swap can now be discarded,
  * to allow the swap device to optimize its wear-levelling.
  */
 static void discard_swap_cluster(struct swap_info_struct *si,
                  pgoff_t start_page, pgoff_t nr_pages)
 {
     struct swap_extent *se = offset_to_swap_extent(si, start_page);
 
     while (nr_pages) {
         pgoff_t offset = start_page - se->start_page;
         sector_t start_block = se->start_block + offset;
         sector_t nr_blocks = se->nr_pages - offset;
 
         if (nr_blocks > nr_pages)
             nr_blocks = nr_pages;
         start_page += nr_blocks;
         nr_pages -= nr_blocks;
 
         start_block <<= PAGE_SHIFT - 9;
         nr_blocks <<= PAGE_SHIFT - 9;
         if (blkdev_issue_discard(si->bdev, start_block,
                     nr_blocks, GFP_NOIO))
             break;
 
         se = next_se(se);
     }
 }
 
 #ifdef CONFIG_THP_SWAP
 #define SWAPFILE_CLUSTER    HPAGE_PMD_NR
 
 #define swap_entry_size(size)   (size)
 #else
 #define SWAPFILE_CLUSTER    256
 
 /*
  * Define swap_entry_size() as constant to let compiler to optimize
  * out some code if !CONFIG_THP_SWAP
  */
 #define swap_entry_size(size)   1
 #endif
 #define LATENCY_LIMIT       256
 
 static inline void cluster_set_flag(struct swap_cluster_info *info,
     unsigned int flag)
 {
     info->flags = flag;
 }
 
 static inline unsigned int cluster_count(struct swap_cluster_info *info)
 {
     return info->data;
 }
 
 static inline void cluster_set_count(struct swap_cluster_info *info,
                      unsigned int c)
 {
     info->data = c;
 }
 
 static inline void cluster_set_count_flag(struct swap_cluster_info *info,
                      unsigned int c, unsigned int f)
 {
     info->flags = f;
     info->data = c;
 }
 
 static inline unsigned int cluster_next(struct swap_cluster_info *info)
 {
     return info->data;
 }
 
 static inline void cluster_set_next(struct swap_cluster_info *info,
                     unsigned int n)
 {
     info->data = n;
 }
 
 static inline void cluster_set_next_flag(struct swap_cluster_info *info,
                      unsigned int n, unsigned int f)
 {
     info->flags = f;
     info->data = n;
 }
 
 static inline bool cluster_is_free(struct swap_cluster_info *info)
 {
     return info->flags & CLUSTER_FLAG_FREE;
 }
 
 static inline bool cluster_is_null(struct swap_cluster_info *info)
 {
     return info->flags & CLUSTER_FLAG_NEXT_NULL;
 }
 
 static inline void cluster_set_null(struct swap_cluster_info *info)
 {
     info->flags = CLUSTER_FLAG_NEXT_NULL;
     info->data = 0;
 }
 
 static inline bool cluster_is_huge(struct swap_cluster_info *info)
 {
     if (IS_ENABLED(CONFIG_THP_SWAP))
         return info->flags & CLUSTER_FLAG_HUGE;
     return false;
 }
 
 static inline void cluster_clear_huge(struct swap_cluster_info *info)
 {
     info->flags &= ~CLUSTER_FLAG_HUGE;
 }
 
 static inline struct swap_cluster_info *lock_cluster(struct swap_info_struct *si,
                              unsigned long offset)
 {
     struct swap_cluster_info *ci;
 
     ci = si->cluster_info;
     if (ci) {
         ci += offset / SWAPFILE_CLUSTER;
         spin_lock(&ci->lock);
     }
     return ci;
 }
 
 static inline void unlock_cluster(struct swap_cluster_info *ci)
 {
     if (ci)
         spin_unlock(&ci->lock);
 }
 
 /*
  * Determine the locking method in use for this device.  Return
  * swap_cluster_info if SSD-style cluster-based locking is in place.
  */
 static inline struct swap_cluster_info *lock_cluster_or_swap_info(
         struct swap_info_struct *si, unsigned long offset)
 {
     struct swap_cluster_info *ci;
 
     /* Try to use fine-grained SSD-style locking if available: */
     ci = lock_cluster(si, offset);
     /* Otherwise, fall back to traditional, coarse locking: */
     if (!ci)
         spin_lock(&si->lock);
 
     return ci;
 }
 
 static inline void unlock_cluster_or_swap_info(struct swap_info_struct *si,
                            struct swap_cluster_info *ci)
 {
     if (ci)
         unlock_cluster(ci);
     else
         spin_unlock(&si->lock);
 }
 
 static inline bool cluster_list_empty(struct swap_cluster_list *list)
 {
     return cluster_is_null(&list->head);
 }
 
 static inline unsigned int cluster_list_first(struct swap_cluster_list *list)
 {
     return cluster_next(&list->head);
 }
 
 static void cluster_list_init(struct swap_cluster_list *list)
 {
     cluster_set_null(&list->head);
     cluster_set_null(&list->tail);
 }
 
 static void cluster_list_add_tail(struct swap_cluster_list *list,
                   struct swap_cluster_info *ci,
                   unsigned int idx)
 {
     if (cluster_list_empty(list)) {
         cluster_set_next_flag(&list->head, idx, 0);
         cluster_set_next_flag(&list->tail, idx, 0);
     } else {
         struct swap_cluster_info *ci_tail;
         unsigned int tail = cluster_next(&list->tail);
 
         /*
          * Nested cluster lock, but both cluster locks are
          * only acquired when we held swap_info_struct->lock
          */
         ci_tail = ci + tail;
         spin_lock_nested(&ci_tail->lock, SINGLE_DEPTH_NESTING);
         cluster_set_next(ci_tail, idx);
         spin_unlock(&ci_tail->lock);
         cluster_set_next_flag(&list->tail, idx, 0);
     }
 }
 
 static unsigned int cluster_list_del_first(struct swap_cluster_list *list,
                        struct swap_cluster_info *ci)
 {
     unsigned int idx;
 
     idx = cluster_next(&list->head);
     if (cluster_next(&list->tail) == idx) {
         cluster_set_null(&list->head);
         cluster_set_null(&list->tail);
     } else
         cluster_set_next_flag(&list->head,
                       cluster_next(&ci[idx]), 0);
 
     return idx;
 }
 
 /* Add a cluster to discard list and schedule it to do discard */
 static void swap_cluster_schedule_discard(struct swap_info_struct *si,
         unsigned int idx)
 {
     /*
      * If scan_swap_map_slots() can't find a free cluster, it will check
      * si->swap_map directly. To make sure the discarding cluster isn't
      * taken by scan_swap_map_slots(), mark the swap entries bad (occupied).
      * It will be cleared after discard
      */
     memset(si->swap_map + idx * SWAPFILE_CLUSTER,
             SWAP_MAP_BAD, SWAPFILE_CLUSTER);
 
     cluster_list_add_tail(&si->discard_clusters, si->cluster_info, idx);
 
     schedule_work(&si->discard_work);
 }
 
 static void __free_cluster(struct swap_info_struct *si, unsigned long idx)
 {
     struct swap_cluster_info *ci = si->cluster_info;
 
     cluster_set_flag(ci + idx, CLUSTER_FLAG_FREE);
     cluster_list_add_tail(&si->free_clusters, ci, idx);
 }
 
 /*
  * Doing discard actually. After a cluster discard is finished, the cluster
  * will be added to free cluster list. caller should hold si->lock.
 */
 static void swap_do_scheduled_discard(struct swap_info_struct *si)
 {
     struct swap_cluster_info *info, *ci;
     unsigned int idx;
 
     info = si->cluster_info;
 
     while (!cluster_list_empty(&si->discard_clusters)) {
         idx = cluster_list_del_first(&si->discard_clusters, info);
         spin_unlock(&si->lock);
 
         discard_swap_cluster(si, idx * SWAPFILE_CLUSTER,
                 SWAPFILE_CLUSTER);
 
         spin_lock(&si->lock);
         ci = lock_cluster(si, idx * SWAPFILE_CLUSTER);
         __free_cluster(si, idx);
         memset(si->swap_map + idx * SWAPFILE_CLUSTER,
                 0, SWAPFILE_CLUSTER);
         unlock_cluster(ci);
     }
 }
 
 static void swap_discard_work(struct work_struct *work)
 {
     struct swap_info_struct *si;
 
     si = container_of(work, struct swap_info_struct, discard_work);
 
     spin_lock(&si->lock);
     swap_do_scheduled_discard(si);
     spin_unlock(&si->lock);
 }
 
 static void swap_users_ref_free(struct percpu_ref *ref)
 {
     struct swap_info_struct *si;
 
     si = container_of(ref, struct swap_info_struct, users);
     complete(&si->comp);
 }
 
 static void alloc_cluster(struct swap_info_struct *si, unsigned long idx)
 {
     struct swap_cluster_info *ci = si->cluster_info;
 
     VM_BUG_ON(cluster_list_first(&si->free_clusters) != idx);
     cluster_list_del_first(&si->free_clusters, ci);
     cluster_set_count_flag(ci + idx, 0, 0);
 }
 
 static void free_cluster(struct swap_info_struct *si, unsigned long idx)
 {
     struct swap_cluster_info *ci = si->cluster_info + idx;
 
     VM_BUG_ON(cluster_count(ci) != 0);
     /*
      * If the swap is discardable, prepare discard the cluster
      * instead of free it immediately. The cluster will be freed
      * after discard.
      */
     if ((si->flags & (SWP_WRITEOK | SWP_PAGE_DISCARD)) ==
         (SWP_WRITEOK | SWP_PAGE_DISCARD)) {
         swap_cluster_schedule_discard(si, idx);
         return;
     }
 
     __free_cluster(si, idx);
 }
 
 /*
  * The cluster corresponding to page_nr will be used. The cluster will be
  * removed from free cluster list and its usage counter will be increased.
  */
 static void inc_cluster_info_page(struct swap_info_struct *p,
     struct swap_cluster_info *cluster_info, unsigned long page_nr)
 {
     unsigned long idx = page_nr / SWAPFILE_CLUSTER;
 
     if (!cluster_info)
         return;
     if (cluster_is_free(&cluster_info[idx]))
         alloc_cluster(p, idx);
 
     VM_BUG_ON(cluster_count(&cluster_info[idx]) >= SWAPFILE_CLUSTER);
     cluster_set_count(&cluster_info[idx],
         cluster_count(&cluster_info[idx]) + 1);
 }
 
 /*
  * The cluster corresponding to page_nr decreases one usage. If the usage
  * counter becomes 0, which means no page in the cluster is in using, we can
  * optionally discard the cluster and add it to free cluster list.
  */
 static void dec_cluster_info_page(struct swap_info_struct *p,
     struct swap_cluster_info *cluster_info, unsigned long page_nr)
 {
     unsigned long idx = page_nr / SWAPFILE_CLUSTER;
 
     if (!cluster_info)
         return;
 
     VM_BUG_ON(cluster_count(&cluster_info[idx]) == 0);
     cluster_set_count(&cluster_info[idx],
         cluster_count(&cluster_info[idx]) - 1);
 
     if (cluster_count(&cluster_info[idx]) == 0)
         free_cluster(p, idx);
 }
 
 /*
  * It's possible scan_swap_map_slots() uses a free cluster in the middle of free
  * cluster list. Avoiding such abuse to avoid list corruption.
  */
 static bool
 scan_swap_map_ssd_cluster_conflict(struct swap_info_struct *si,
     unsigned long offset)
 {
     struct percpu_cluster *percpu_cluster;
     bool conflict;
 
     offset /= SWAPFILE_CLUSTER;
     conflict = !cluster_list_empty(&si->free_clusters) &&
         offset != cluster_list_first(&si->free_clusters) &&
         cluster_is_free(&si->cluster_info[offset]);
 
     if (!conflict)
         return false;
 
     percpu_cluster = this_cpu_ptr(si->percpu_cluster);
     cluster_set_null(&percpu_cluster->index);
     return true;
 }
 
 /*
  * Try to get a swap entry from current cpu's swap entry pool (a cluster). This
  * might involve allocating a new cluster for current CPU too.
  */
 static bool scan_swap_map_try_ssd_cluster(struct swap_info_struct *si,
     unsigned long *offset, unsigned long *scan_base)
 {
     struct percpu_cluster *cluster;
     struct swap_cluster_info *ci;
     unsigned long tmp, max;
 
 new_cluster:
     cluster = this_cpu_ptr(si->percpu_cluster);
     if (cluster_is_null(&cluster->index)) {
         if (!cluster_list_empty(&si->free_clusters)) {
             cluster->index = si->free_clusters.head;
             cluster->next = cluster_next(&cluster->index) *
                     SWAPFILE_CLUSTER;
         } else if (!cluster_list_empty(&si->discard_clusters)) {
             /*
              * we don't have free cluster but have some clusters in
              * discarding, do discard now and reclaim them, then
              * reread cluster_next_cpu since we dropped si->lock
              */
             swap_do_scheduled_discard(si);
             *scan_base = this_cpu_read(*si->cluster_next_cpu);
             *offset = *scan_base;
             goto new_cluster;
         } else
             return false;
     }
 
     /*
      * Other CPUs can use our cluster if they can't find a free cluster,
      * check if there is still free entry in the cluster
      */
     tmp = cluster->next;
     max = min_t(unsigned long, si->max,
             (cluster_next(&cluster->index) + 1) * SWAPFILE_CLUSTER);
     if (tmp < max) {
         ci = lock_cluster(si, tmp);
         while (tmp < max) {
             if (!si->swap_map[tmp])
                 break;
             tmp++;
         }
         unlock_cluster(ci);
     }
     if (tmp >= max) {
         cluster_set_null(&cluster->index);
         goto new_cluster;
     }
     cluster->next = tmp + 1;
     *offset = tmp;
     *scan_base = tmp;
     return true;
 }
 
 static void __del_from_avail_list(struct swap_info_struct *p)
 {
     int nid;
 
     for_each_node(nid)
         plist_del(&p->avail_lists[nid], &swap_avail_heads[nid]);
 }
 
 static void del_from_avail_list(struct swap_info_struct *p)
 {
     spin_lock(&swap_avail_lock);
     __del_from_avail_list(p);
     spin_unlock(&swap_avail_lock);
 }
 
 static void swap_range_alloc(struct swap_info_struct *si, unsigned long offset,
                  unsigned int nr_entries)
 {
     unsigned int end = offset + nr_entries - 1;
 
     if (offset == si->lowest_bit)
         si->lowest_bit += nr_entries;
     if (end == si->highest_bit)
         WRITE_ONCE(si->highest_bit, si->highest_bit - nr_entries);
     WRITE_ONCE(si->inuse_pages, si->inuse_pages + nr_entries);
     if (si->inuse_pages == si->pages) {
         si->lowest_bit = si->max;
         si->highest_bit = 0;
         del_from_avail_list(si);
     }
 }
 
 static void add_to_avail_list(struct swap_info_struct *p)
 {
     int nid;
 
     spin_lock(&swap_avail_lock);
     for_each_node(nid) {
         WARN_ON(!plist_node_empty(&p->avail_lists[nid]));
         plist_add(&p->avail_lists[nid], &swap_avail_heads[nid]);
     }
     spin_unlock(&swap_avail_lock);
 }
 
 static void swap_range_free(struct swap_info_struct *si, unsigned long offset,
                 unsigned int nr_entries)
 {
     unsigned long begin = offset;
     unsigned long end = offset + nr_entries - 1;
     void (*swap_slot_free_notify)(struct block_device *, unsigned long);
 
     if (offset < si->lowest_bit)
         si->lowest_bit = offset;
     if (end > si->highest_bit) {
         bool was_full = !si->highest_bit;
 
         WRITE_ONCE(si->highest_bit, end);
         if (was_full && (si->flags & SWP_WRITEOK))
             add_to_avail_list(si);
     }
     atomic_long_add(nr_entries, &nr_swap_pages);
     WRITE_ONCE(si->inuse_pages, si->inuse_pages - nr_entries);
     if (si->flags & SWP_BLKDEV)
         swap_slot_free_notify =
             si->bdev->bd_disk->fops->swap_slot_free_notify;
     else
         swap_slot_free_notify = NULL;
     while (offset <= end) {
         arch_swap_invalidate_page(si->type, offset);
         frontswap_invalidate_page(si->type, offset);
         if (swap_slot_free_notify)
             swap_slot_free_notify(si->bdev, offset);
         offset++;
     }
     clear_shadow_from_swap_cache(si->type, begin, end);
 }
 
 static void set_cluster_next(struct swap_info_struct *si, unsigned long next)
 {
     unsigned long prev;
 
     if (!(si->flags & SWP_SOLIDSTATE)) {
         si->cluster_next = next;
         return;
     }
 
     prev = this_cpu_read(*si->cluster_next_cpu);
     /*
      * Cross the swap address space size aligned trunk, choose
      * another trunk randomly to avoid lock contention on swap
      * address space if possible.
      */
     if ((prev >> SWAP_ADDRESS_SPACE_SHIFT) !=
         (next >> SWAP_ADDRESS_SPACE_SHIFT)) {
         /* No free swap slots available */
         if (si->highest_bit <= si->lowest_bit)
             return;
         next = si->lowest_bit +
             prandom_u32_max(si->highest_bit - si->lowest_bit + 1);
         next = ALIGN_DOWN(next, SWAP_ADDRESS_SPACE_PAGES);
         next = max_t(unsigned int, next, si->lowest_bit);
     }
     this_cpu_write(*si->cluster_next_cpu, next);
 }
 
 static bool swap_offset_available_and_locked(struct swap_info_struct *si,
                          unsigned long offset)
 {
     if (data_race(!si->swap_map[offset])) {
         spin_lock(&si->lock);
         return true;
     }
 
     if (vm_swap_full() && READ_ONCE(si->swap_map[offset]) == SWAP_HAS_CACHE) {
         spin_lock(&si->lock);
         return true;
     }
 
     return false;
 }
 
 static int scan_swap_map_slots(struct swap_info_struct *si,
                    unsigned char usage, int nr,
                    swp_entry_t slots[])
 {
     struct swap_cluster_info *ci;
     unsigned long offset;
     unsigned long scan_base;
     unsigned long last_in_cluster = 0;
     int latency_ration = LATENCY_LIMIT;
     int n_ret = 0;
     bool scanned_many = false;
 
     /*
      * We try to cluster swap pages by allocating them sequentially
      * in swap.  Once we've allocated SWAPFILE_CLUSTER pages this
      * way, however, we resort to first-free allocation, starting
      * a new cluster.  This prevents us from scattering swap pages
      * all over the entire swap partition, so that we reduce
      * overall disk seek times between swap pages.  -- sct
      * But we do now try to find an empty cluster.  -Andrea
      * And we let swap pages go all over an SSD partition.  Hugh
      */
 
     si->flags += SWP_SCANNING;
     /*
      * Use percpu scan base for SSD to reduce lock contention on
      * cluster and swap cache.  For HDD, sequential access is more
      * important.
      */
     if (si->flags & SWP_SOLIDSTATE)
         scan_base = this_cpu_read(*si->cluster_next_cpu);
     else
         scan_base = si->cluster_next;
     offset = scan_base;
 
     /* SSD algorithm */
     if (si->cluster_info) {
         if (!scan_swap_map_try_ssd_cluster(si, &offset, &scan_base))
             goto scan;
     } else if (unlikely(!si->cluster_nr--)) {
         if (si->pages - si->inuse_pages < SWAPFILE_CLUSTER) {
             si->cluster_nr = SWAPFILE_CLUSTER - 1;
             goto checks;
         }
 
         spin_unlock(&si->lock);
 
         /*
          * If seek is expensive, start searching for new cluster from
          * start of partition, to minimize the span of allocated swap.
          * If seek is cheap, that is the SWP_SOLIDSTATE si->cluster_info
          * case, just handled by scan_swap_map_try_ssd_cluster() above.
          */
         scan_base = offset = si->lowest_bit;
         last_in_cluster = offset + SWAPFILE_CLUSTER - 1;
 
         /* Locate the first empty (unaligned) cluster */
         for (; last_in_cluster <= si->highest_bit; offset++) {
             if (si->swap_map[offset])
                 last_in_cluster = offset + SWAPFILE_CLUSTER;
             else if (offset == last_in_cluster) {
                 spin_lock(&si->lock);
                 offset -= SWAPFILE_CLUSTER - 1;
                 si->cluster_next = offset;
                 si->cluster_nr = SWAPFILE_CLUSTER - 1;
                 goto checks;
             }
             if (unlikely(--latency_ration < 0)) {
                 cond_resched();
                 latency_ration = LATENCY_LIMIT;
             }
         }
 
         offset = scan_base;
         spin_lock(&si->lock);
         si->cluster_nr = SWAPFILE_CLUSTER - 1;
     }
 
 checks:
     if (si->cluster_info) {
         while (scan_swap_map_ssd_cluster_conflict(si, offset)) {
         /* take a break if we already got some slots */
             if (n_ret)
                 goto done;
             if (!scan_swap_map_try_ssd_cluster(si, &offset,
                             &scan_base))
                 goto scan;
         }
     }
     if (!(si->flags & SWP_WRITEOK))
         goto no_page;
     if (!si->highest_bit)
         goto no_page;
     if (offset > si->highest_bit)
         scan_base = offset = si->lowest_bit;
 
     ci = lock_cluster(si, offset);
     /* reuse swap entry of cache-only swap if not busy. */
     if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
         int swap_was_freed;
         unlock_cluster(ci);
         spin_unlock(&si->lock);
         swap_was_freed = __try_to_reclaim_swap(si, offset, TTRS_ANYWAY);
         spin_lock(&si->lock);
         /* entry was freed successfully, try to use this again */
         if (swap_was_freed)
             goto checks;
         goto scan; /* check next one */
     }
 
     if (si->swap_map[offset]) {
         unlock_cluster(ci);
         if (!n_ret)
             goto scan;
         else
             goto done;
     }
     WRITE_ONCE(si->swap_map[offset], usage);
     inc_cluster_info_page(si, si->cluster_info, offset);
     unlock_cluster(ci);
 
     swap_range_alloc(si, offset, 1);
     slots[n_ret++] = swp_entry(si->type, offset);
 
     /* got enough slots or reach max slots? */
     if ((n_ret == nr) || (offset >= si->highest_bit))
         goto done;
 
     /* search for next available slot */
 
     /* time to take a break? */
     if (unlikely(--latency_ration < 0)) {
         if (n_ret)
             goto done;
         spin_unlock(&si->lock);
         cond_resched();
         spin_lock(&si->lock);
         latency_ration = LATENCY_LIMIT;
     }
 
     /* try to get more slots in cluster */
     if (si->cluster_info) {
         if (scan_swap_map_try_ssd_cluster(si, &offset, &scan_base))
             goto checks;
     } else if (si->cluster_nr && !si->swap_map[++offset]) {
         /* non-ssd case, still more slots in cluster? */
         --si->cluster_nr;
         goto checks;
     }
 
     /*
      * Even if there's no free clusters available (fragmented),
      * try to scan a little more quickly with lock held unless we
      * have scanned too many slots already.
      */
     if (!scanned_many) {
         unsigned long scan_limit;
 
         if (offset < scan_base)
             scan_limit = scan_base;
         else
             scan_limit = si->highest_bit;
         for (; offset <= scan_limit && --latency_ration > 0;
              offset++) {
             if (!si->swap_map[offset])
                 goto checks;
         }
     }
 
 done:
     set_cluster_next(si, offset + 1);
     si->flags -= SWP_SCANNING;
     return n_ret;
 
 scan:
     spin_unlock(&si->lock);
     while (++offset <= READ_ONCE(si->highest_bit)) {
         if (swap_offset_available_and_locked(si, offset))
             goto checks;
         if (unlikely(--latency_ration < 0)) {
             cond_resched();
             latency_ration = LATENCY_LIMIT;
             scanned_many = true;
         }
     }
     offset = si->lowest_bit;
     while (offset < scan_base) {
         if (swap_offset_available_and_locked(si, offset))
             goto checks;
         if (unlikely(--latency_ration < 0)) {
             cond_resched();
             latency_ration = LATENCY_LIMIT;
             scanned_many = true;
         }
         offset++;
     }
     spin_lock(&si->lock);
 
 no_page:
     si->flags -= SWP_SCANNING;
     return n_ret;
 }
 
 static int swap_alloc_cluster(struct swap_info_struct *si, swp_entry_t *slot)
 {
     unsigned long idx;
     struct swap_cluster_info *ci;
     unsigned long offset;
 
     /*
      * Should not even be attempting cluster allocations when huge
      * page swap is disabled.  Warn and fail the allocation.
      */
     if (!IS_ENABLED(CONFIG_THP_SWAP)) {
         VM_WARN_ON_ONCE(1);
         return 0;
     }
 
     if (cluster_list_empty(&si->free_clusters))
         return 0;
 
     idx = cluster_list_first(&si->free_clusters);
     offset = idx * SWAPFILE_CLUSTER;
     ci = lock_cluster(si, offset);
     alloc_cluster(si, idx);
     cluster_set_count_flag(ci, SWAPFILE_CLUSTER, CLUSTER_FLAG_HUGE);
 
     memset(si->swap_map + offset, SWAP_HAS_CACHE, SWAPFILE_CLUSTER);
     unlock_cluster(ci);
     swap_range_alloc(si, offset, SWAPFILE_CLUSTER);
     *slot = swp_entry(si->type, offset);
 
     return 1;
 }
 
 static void swap_free_cluster(struct swap_info_struct *si, unsigned long idx)
 {
     unsigned long offset = idx * SWAPFILE_CLUSTER;
     struct swap_cluster_info *ci;
 
     ci = lock_cluster(si, offset);
     memset(si->swap_map + offset, 0, SWAPFILE_CLUSTER);
     cluster_set_count_flag(ci, 0, 0);
     free_cluster(si, idx);
     unlock_cluster(ci);
     swap_range_free(si, offset, SWAPFILE_CLUSTER);
 }
 
 int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_size)
 {
     unsigned long size = swap_entry_size(entry_size);
     struct swap_info_struct *si, *next;
     long avail_pgs;
     int n_ret = 0;
     int node;
 
     /* Only single cluster request supported */
     WARN_ON_ONCE(n_goal > 1 && size == SWAPFILE_CLUSTER);
 
     spin_lock(&swap_avail_lock);
 
     avail_pgs = atomic_long_read(&nr_swap_pages) / size;
     if (avail_pgs <= 0) {
         spin_unlock(&swap_avail_lock);
         goto noswap;
     }
 
     n_goal = min3((long)n_goal, (long)SWAP_BATCH, avail_pgs);
 
     atomic_long_sub(n_goal * size, &nr_swap_pages);
 
 start_over:
     node = numa_node_id();
     plist_for_each_entry_safe(si, next, &swap_avail_heads[node], avail_lists[node]) {
         /* requeue si to after same-priority siblings */
         plist_requeue(&si->avail_lists[node], &swap_avail_heads[node]);
         spin_unlock(&swap_avail_lock);
         spin_lock(&si->lock);
         if (!si->highest_bit || !(si->flags & SWP_WRITEOK)) {
             spin_lock(&swap_avail_lock);
             if (plist_node_empty(&si->avail_lists[node])) {
                 spin_unlock(&si->lock);
                 goto nextsi;
             }
             WARN(!si->highest_bit,
                  "swap_info %d in list but !highest_bit\n",
                  si->type);
             WARN(!(si->flags & SWP_WRITEOK),
                  "swap_info %d in list but !SWP_WRITEOK\n",
                  si->type);
             __del_from_avail_list(si);
             spin_unlock(&si->lock);
             goto nextsi;
         }
         if (size == SWAPFILE_CLUSTER) {
             if (si->flags & SWP_BLKDEV)
                 n_ret = swap_alloc_cluster(si, swp_entries);
         } else
             n_ret = scan_swap_map_slots(si, SWAP_HAS_CACHE,
                             n_goal, swp_entries);
         spin_unlock(&si->lock);
         if (n_ret || size == SWAPFILE_CLUSTER)
             goto check_out;
         pr_debug("scan_swap_map of si %d failed to find offset\n",
             si->type);
 
         spin_lock(&swap_avail_lock);
 nextsi:
         /*
          * if we got here, it's likely that si was almost full before,
          * and since scan_swap_map_slots() can drop the si->lock,
          * multiple callers probably all tried to get a page from the
          * same si and it filled up before we could get one; or, the si
          * filled up between us dropping swap_avail_lock and taking
          * si->lock. Since we dropped the swap_avail_lock, the
          * swap_avail_head list may have been modified; so if next is
          * still in the swap_avail_head list then try it, otherwise
          * start over if we have not gotten any slots.
          */
         if (plist_node_empty(&next->avail_lists[node]))
             goto start_over;
     }
 
     spin_unlock(&swap_avail_lock);
 
 check_out:
     if (n_ret < n_goal)
         atomic_long_add((long)(n_goal - n_ret) * size,
                 &nr_swap_pages);
 noswap:
     return n_ret;
 }
 
 static struct swap_info_struct *_swap_info_get(swp_entry_t entry)
 {
     struct swap_info_struct *p;
     unsigned long offset;
 
     if (!entry.val)
         goto out;
     p = swp_swap_info(entry);
     if (!p)
         goto bad_nofile;
     if (data_race(!(p->flags & SWP_USED)))
         goto bad_device;
     offset = swp_offset(entry);
     if (offset >= p->max)
         goto bad_offset;
     if (data_race(!p->swap_map[swp_offset(entry)]))
         goto bad_free;
     return p;
 
 bad_free:
     pr_err("%s: %s%08lx\n", __func__, Unused_offset, entry.val);
     goto out;
 bad_offset:
     pr_err("%s: %s%08lx\n", __func__, Bad_offset, entry.val);
     goto out;
 bad_device:
     pr_err("%s: %s%08lx\n", __func__, Unused_file, entry.val);
     goto out;
 bad_nofile:
     pr_err("%s: %s%08lx\n", __func__, Bad_file, entry.val);
 out:
     return NULL;
 }
 
 static struct swap_info_struct *swap_info_get_cont(swp_entry_t entry,
                     struct swap_info_struct *q)
 {
     struct swap_info_struct *p;
 
     p = _swap_info_get(entry);
 
     if (p != q) {
         if (q != NULL)
             spin_unlock(&q->lock);
         if (p != NULL)
             spin_lock(&p->lock);
     }
     return p;
 }
 
 static unsigned char __swap_entry_free_locked(struct swap_info_struct *p,
                           unsigned long offset,
                           unsigned char usage)
 {
     unsigned char count;
     unsigned char has_cache;
 
     count = p->swap_map[offset];
 
     has_cache = count & SWAP_HAS_CACHE;
     count &= ~SWAP_HAS_CACHE;
 
     if (usage == SWAP_HAS_CACHE) {
         VM_BUG_ON(!has_cache);
         has_cache = 0;
     } else if (count == SWAP_MAP_SHMEM) {
         /*
          * Or we could insist on shmem.c using a special
          * swap_shmem_free() and free_shmem_swap_and_cache()...
          */
         count = 0;
     } else if ((count & ~COUNT_CONTINUED) <= SWAP_MAP_MAX) {
         if (count == COUNT_CONTINUED) {
             if (swap_count_continued(p, offset, count))
                 count = SWAP_MAP_MAX | COUNT_CONTINUED;
             else
                 count = SWAP_MAP_MAX;
         } else
             count--;
     }
 
     usage = count | has_cache;
     if (usage)
         WRITE_ONCE(p->swap_map[offset], usage);
     else
         WRITE_ONCE(p->swap_map[offset], SWAP_HAS_CACHE);
 
     return usage;
 }
 
 /*
  * Check whether swap entry is valid in the swap device.  If so,
  * return pointer to swap_info_struct, and keep the swap entry valid
  * via preventing the swap device from being swapoff, until
  * put_swap_device() is called.  Otherwise return NULL.
  *
  * Notice that swapoff or swapoff+swapon can still happen before the
  * percpu_ref_tryget_live() in get_swap_device() or after the
  * percpu_ref_put() in put_swap_device() if there isn't any other way
  * to prevent swapoff, such as page lock, page table lock, etc.  The
  * caller must be prepared for that.  For example, the following
  * situation is possible.
  *
  *   CPU1               CPU2
  *   do_swap_page()
  *     ...              swapoff+swapon
  *     __read_swap_cache_async()
  *       swapcache_prepare()
  *         __swap_duplicate()
  *           // check swap_map
  *     // verify PTE not changed
  *
  * In __swap_duplicate(), the swap_map need to be checked before
  * changing partly because the specified swap entry may be for another
  * swap device which has been swapoff.  And in do_swap_page(), after
  * the page is read from the swap device, the PTE is verified not
  * changed with the page table locked to check whether the swap device
  * has been swapoff or swapoff+swapon.
  */
 struct swap_info_struct *get_swap_device(swp_entry_t entry)
 {
     struct swap_info_struct *si;
     unsigned long offset;
 
     if (!entry.val)
         goto out;
     si = swp_swap_info(entry);
     if (!si)
         goto bad_nofile;
     if (!percpu_ref_tryget_live(&si->users))
         goto out;
     /*
      * Guarantee the si->users are checked before accessing other
      * fields of swap_info_struct.
      *
      * Paired with the spin_unlock() after setup_swap_info() in
      * enable_swap_info().
      */
     smp_rmb();
     offset = swp_offset(entry);
     if (offset >= si->max)
         goto put_out;
 
     return si;
 bad_nofile:
     pr_err("%s: %s%08lx\n", __func__, Bad_file, entry.val);
 out:
     return NULL;
 put_out:
     pr_err("%s: %s%08lx\n", __func__, Bad_offset, entry.val);
     percpu_ref_put(&si->users);
     return NULL;
 }
 
 static unsigned char __swap_entry_free(struct swap_info_struct *p,
                        swp_entry_t entry)
 {
     struct swap_cluster_info *ci;
     unsigned long offset = swp_offset(entry);
     unsigned char usage;
 
     ci = lock_cluster_or_swap_info(p, offset);
     usage = __swap_entry_free_locked(p, offset, 1);
     unlock_cluster_or_swap_info(p, ci);
     if (!usage)
         free_swap_slot(entry);
 
     return usage;
 }
 
 static void swap_entry_free(struct swap_info_struct *p, swp_entry_t entry)
 {
     struct swap_cluster_info *ci;
     unsigned long offset = swp_offset(entry);
     unsigned char count;
 
     ci = lock_cluster(p, offset);
     count = p->swap_map[offset];
     VM_BUG_ON(count != SWAP_HAS_CACHE);
     p->swap_map[offset] = 0;
     dec_cluster_info_page(p, p->cluster_info, offset);
     unlock_cluster(ci);
 
     mem_cgroup_uncharge_swap(entry, 1);
     swap_range_free(p, offset, 1);
 }
 
 /*
  * Caller has made sure that the swap device corresponding to entry
  * is still around or has not been recycled.
  */
 void swap_free(swp_entry_t entry)
 {
     struct swap_info_struct *p;
 
     p = _swap_info_get(entry);
     if (p)
         __swap_entry_free(p, entry);
 }
 
 /*
  * Called after dropping swapcache to decrease refcnt to swap entries.
  */
 void put_swap_page(struct page *page, swp_entry_t entry)
 {
     unsigned long offset = swp_offset(entry);
     unsigned long idx = offset / SWAPFILE_CLUSTER;
     struct swap_cluster_info *ci;
     struct swap_info_struct *si;
     unsigned char *map;
     unsigned int i, free_entries = 0;
     unsigned char val;
     int size = swap_entry_size(thp_nr_pages(page));
 
     si = _swap_info_get(entry);
     if (!si)
         return;
 
     ci = lock_cluster_or_swap_info(si, offset);
     if (size == SWAPFILE_CLUSTER) {
         VM_BUG_ON(!cluster_is_huge(ci));
         map = si->swap_map + offset;
         for (i = 0; i < SWAPFILE_CLUSTER; i++) {
             val = map[i];
             VM_BUG_ON(!(val & SWAP_HAS_CACHE));
             if (val == SWAP_HAS_CACHE)
                 free_entries++;
         }
         cluster_clear_huge(ci);
         if (free_entries == SWAPFILE_CLUSTER) {
             unlock_cluster_or_swap_info(si, ci);
             spin_lock(&si->lock);
             mem_cgroup_uncharge_swap(entry, SWAPFILE_CLUSTER);
             swap_free_cluster(si, idx);
             spin_unlock(&si->lock);
             return;
         }
     }
     for (i = 0; i < size; i++, entry.val++) {
         if (!__swap_entry_free_locked(si, offset + i, SWAP_HAS_CACHE)) {
             unlock_cluster_or_swap_info(si, ci);
             free_swap_slot(entry);
             if (i == size - 1)
                 return;
             lock_cluster_or_swap_info(si, offset);
         }
     }
     unlock_cluster_or_swap_info(si, ci);
 }
 
 #ifdef CONFIG_THP_SWAP
 int split_swap_cluster(swp_entry_t entry)
 {
     struct swap_info_struct *si;
     struct swap_cluster_info *ci;
     unsigned long offset = swp_offset(entry);
 
     si = _swap_info_get(entry);
     if (!si)
         return -EBUSY;
     ci = lock_cluster(si, offset);
     cluster_clear_huge(ci);
     unlock_cluster(ci);
     return 0;
 }
 #endif
 
 static int swp_entry_cmp(const void *ent1, const void *ent2)
 {
     const swp_entry_t *e1 = ent1, *e2 = ent2;
 
     return (int)swp_type(*e1) - (int)swp_type(*e2);
 }
 
 void swapcache_free_entries(swp_entry_t *entries, int n)
 {
     struct swap_info_struct *p, *prev;
     int i;
 
     if (n <= 0)
         return;
 
     prev = NULL;
     p = NULL;
 
     /*
      * Sort swap entries by swap device, so each lock is only taken once.
      * nr_swapfiles isn't absolutely correct, but the overhead of sort() is
      * so low that it isn't necessary to optimize further.
      */
     if (nr_swapfiles > 1)
         sort(entries, n, sizeof(entries[0]), swp_entry_cmp, NULL);
     for (i = 0; i < n; ++i) {
         p = swap_info_get_cont(entries[i], prev);
         if (p)
             swap_entry_free(p, entries[i]);
         prev = p;
     }
     if (p)
         spin_unlock(&p->lock);
 }
 
 /*
  * How many references to page are currently swapped out?
  * This does not give an exact answer when swap count is continued,
  * but does include the high COUNT_CONTINUED flag to allow for that.
  */
 static int page_swapcount(struct page *page)
 {
     int count = 0;
     struct swap_info_struct *p;
     struct swap_cluster_info *ci;
     swp_entry_t entry;
     unsigned long offset;
 
     entry.val = page_private(page);
     p = _swap_info_get(entry);
     if (p) {
         offset = swp_offset(entry);
         ci = lock_cluster_or_swap_info(p, offset);
         count = swap_count(p->swap_map[offset]);
         unlock_cluster_or_swap_info(p, ci);
     }
     return count;
 }
 
 int __swap_count(swp_entry_t entry)
 {
     struct swap_info_struct *si;
     pgoff_t offset = swp_offset(entry);
     int count = 0;
 
     si = get_swap_device(entry);
     if (si) {
         count = swap_count(si->swap_map[offset]);
         put_swap_device(si);
     }
     return count;
 }
 
 static int swap_swapcount(struct swap_info_struct *si, swp_entry_t entry)
 {
     int count = 0;
     pgoff_t offset = swp_offset(entry);
     struct swap_cluster_info *ci;
 
     ci = lock_cluster_or_swap_info(si, offset);
     count = swap_count(si->swap_map[offset]);
     unlock_cluster_or_swap_info(si, ci);
     return count;
 }
 
 /*
  * How many references to @entry are currently swapped out?
  * This does not give an exact answer when swap count is continued,
  * but does include the high COUNT_CONTINUED flag to allow for that.
  */
 int __swp_swapcount(swp_entry_t entry)
 {
     int count = 0;
     struct swap_info_struct *si;
 
     si = get_swap_device(entry);
     if (si) {
         count = swap_swapcount(si, entry);
         put_swap_device(si);
     }
     return count;
 }
 
 /*
  * How many references to @entry are currently swapped out?
  * This considers COUNT_CONTINUED so it returns exact answer.
  */
 int swp_swapcount(swp_entry_t entry)
 {
     int count, tmp_count, n;
     struct swap_info_struct *p;
     struct swap_cluster_info *ci;
     struct page *page;
     pgoff_t offset;
     unsigned char *map;
 
     p = _swap_info_get(entry);
     if (!p)
         return 0;
 
     offset = swp_offset(entry);
 
     ci = lock_cluster_or_swap_info(p, offset);
 
     count = swap_count(p->swap_map[offset]);
     if (!(count & COUNT_CONTINUED))
         goto out;
 
     count &= ~COUNT_CONTINUED;
     n = SWAP_MAP_MAX + 1;
 
     page = vmalloc_to_page(p->swap_map + offset);
     offset &= ~PAGE_MASK;
     VM_BUG_ON(page_private(page) != SWP_CONTINUED);
 
     do {
         page = list_next_entry(page, lru);
         map = kmap_atomic(page);
         tmp_count = map[offset];
         kunmap_atomic(map);
 
         count += (tmp_count & ~COUNT_CONTINUED) * n;
         n *= (SWAP_CONT_MAX + 1);
     } while (tmp_count & COUNT_CONTINUED);
 out:
     unlock_cluster_or_swap_info(p, ci);
     return count;
 }
 
 static bool swap_page_trans_huge_swapped(struct swap_info_struct *si,
                      swp_entry_t entry)
 {
     struct swap_cluster_info *ci;
     unsigned char *map = si->swap_map;
     unsigned long roffset = swp_offset(entry);
     unsigned long offset = round_down(roffset, SWAPFILE_CLUSTER);
     int i;
     bool ret = false;
 
     ci = lock_cluster_or_swap_info(si, offset);
     if (!ci || !cluster_is_huge(ci)) {
         if (swap_count(map[roffset]))
             ret = true;
         goto unlock_out;
     }
     for (i = 0; i < SWAPFILE_CLUSTER; i++) {
         if (swap_count(map[offset + i])) {
             ret = true;
             break;
         }
     }
 unlock_out:
     unlock_cluster_or_swap_info(si, ci);
     return ret;
 }
 
 static bool folio_swapped(struct folio *folio)
 {
     swp_entry_t entry;
     struct swap_info_struct *si;
 
     if (!IS_ENABLED(CONFIG_THP_SWAP) || likely(!folio_test_large(folio)))
         return page_swapcount(&folio->page) != 0;
 
     entry = folio_swap_entry(folio);
     si = _swap_info_get(entry);
     if (si)
         return swap_page_trans_huge_swapped(si, entry);
     return false;
 }
 
 /*
  * If swap is getting full, or if there are no more mappings of this page,
  * then try_to_free_swap is called to free its swap space.
  */
 int try_to_free_swap(struct page *page)
 {
     struct folio *folio = page_folio(page);
     VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
 
     if (!folio_test_swapcache(folio))
         return 0;
     if (folio_test_writeback(folio))
         return 0;
     if (folio_swapped(folio))
         return 0;
 
     /*
      * Once hibernation has begun to create its image of memory,
      * there's a danger that one of the calls to try_to_free_swap()
      * - most probably a call from __try_to_reclaim_swap() while
      * hibernation is allocating its own swap pages for the image,
      * but conceivably even a call from memory reclaim - will free
      * the swap from a page which has already been recorded in the
      * image as a clean swapcache page, and then reuse its swap for
      * another page of the image.  On waking from hibernation, the
      * original page might be freed under memory pressure, then
      * later read back in from swap, now with the wrong data.
      *
      * Hibernation suspends storage while it is writing the image
      * to disk so check that here.
      */
     if (pm_suspended_storage())
         return 0;
 
     delete_from_swap_cache(folio);
     folio_set_dirty(folio);
     return 1;
 }
 
 /*
  * Free the swap entry like above, but also try to
  * free the page cache entry if it is the last user.
  */
 int free_swap_and_cache(swp_entry_t entry)
 {
     struct swap_info_struct *p;
     unsigned char count;
 
     if (non_swap_entry(entry))
         return 1;
 
     p = _swap_info_get(entry);
     if (p) {
         count = __swap_entry_free(p, entry);
         if (count == SWAP_HAS_CACHE &&
             !swap_page_trans_huge_swapped(p, entry))
             __try_to_reclaim_swap(p, swp_offset(entry),
                           TTRS_UNMAPPED | TTRS_FULL);
     }
     return p != NULL;
 }
 
 #ifdef CONFIG_HIBERNATION
 
 swp_entry_t get_swap_page_of_type(int type)
 {
     struct swap_info_struct *si = swap_type_to_swap_info(type);
     swp_entry_t entry = {0};
 
     if (!si)
         goto fail;
 
     /* This is called for allocating swap entry, not cache */
     spin_lock(&si->lock);
     if ((si->flags & SWP_WRITEOK) && scan_swap_map_slots(si, 1, 1, &entry))
         atomic_long_dec(&nr_swap_pages);
     spin_unlock(&si->lock);
 fail:
     return entry;
 }
 
 /*
  * Find the swap type that corresponds to given device (if any).
  *
  * @offset - number of the PAGE_SIZE-sized block of the device, starting
  * from 0, in which the swap header is expected to be located.
  *
  * This is needed for the suspend to disk (aka swsusp).
  */
 int swap_type_of(dev_t device, sector_t offset)
 {
     int type;
 
     if (!device)
         return -1;
 
     spin_lock(&swap_lock);
     for (type = 0; type < nr_swapfiles; type++) {
         struct swap_info_struct *sis = swap_info[type];
 
         if (!(sis->flags & SWP_WRITEOK))
             continue;
 
         if (device == sis->bdev->bd_dev) {
             struct swap_extent *se = first_se(sis);
 
             if (se->start_block == offset) {
                 spin_unlock(&swap_lock);
                 return type;
             }
         }
     }
     spin_unlock(&swap_lock);
     return -ENODEV;
 }
 
 int find_first_swap(dev_t *device)
 {
     int type;
 
     spin_lock(&swap_lock);
     for (type = 0; type < nr_swapfiles; type++) {
         struct swap_info_struct *sis = swap_info[type];
 
         if (!(sis->flags & SWP_WRITEOK))
             continue;
         *device = sis->bdev->bd_dev;
         spin_unlock(&swap_lock);
         return type;
     }
     spin_unlock(&swap_lock);
     return -ENODEV;
 }
 
 /*
  * Get the (PAGE_SIZE) block corresponding to given offset on the swapdev
  * corresponding to given index in swap_info (swap type).
  */
 sector_t swapdev_block(int type, pgoff_t offset)
 {
     struct swap_info_struct *si = swap_type_to_swap_info(type);
     struct swap_extent *se;
 
     if (!si || !(si->flags & SWP_WRITEOK))
         return 0;
     se = offset_to_swap_extent(si, offset);
     return se->start_block + (offset - se->start_page);
 }
 
 /*
  * Return either the total number of swap pages of given type, or the number
  * of free pages of that type (depending on @free)
  *
  * This is needed for software suspend
  */
 unsigned int count_swap_pages(int type, int free)
 {
     unsigned int n = 0;
 
     spin_lock(&swap_lock);
     if ((unsigned int)type < nr_swapfiles) {
         struct swap_info_struct *sis = swap_info[type];
 
         spin_lock(&sis->lock);
         if (sis->flags & SWP_WRITEOK) {
             n = sis->pages;
             if (free)
                 n -= sis->inuse_pages;
         }
         spin_unlock(&sis->lock);
     }
     spin_unlock(&swap_lock);
     return n;
 }
 #endif /* CONFIG_HIBERNATION */
 
 static inline int pte_same_as_swp(pte_t pte, pte_t swp_pte)
 {
     return pte_same(pte_swp_clear_flags(pte), swp_pte);
 }
 
 /*
  * No need to decide whether this PTE shares the swap entry with others,
  * just let do_wp_page work it out if a write is requested later - to
  * force COW, vm_page_prot omits write permission from any private vma.
  */
 static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
         unsigned long addr, swp_entry_t entry, struct page *page)
 {
     struct page *swapcache;
     spinlock_t *ptl;
     pte_t *pte, new_pte;
     int ret = 1;
 
     swapcache = page;
     page = ksm_might_need_to_copy(page, vma, addr);
     if (unlikely(!page))
         return -ENOMEM;
 
     pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
     if (unlikely(!pte_same_as_swp(*pte, swp_entry_to_pte(entry)))) {
         ret = 0;
         goto out;
     }
 
     if (unlikely(!PageUptodate(page))) {
         pte_t pteval;
 
         dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
         pteval = swp_entry_to_pte(make_swapin_error_entry(page));
         set_pte_at(vma->vm_mm, addr, pte, pteval);
         swap_free(entry);
         ret = 0;
         goto out;
     }
 
     /* See do_swap_page() */
     BUG_ON(!PageAnon(page) && PageMappedToDisk(page));
     BUG_ON(PageAnon(page) && PageAnonExclusive(page));
 
     dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
     inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
     get_page(page);
     if (page == swapcache) {
         rmap_t rmap_flags = RMAP_NONE;
 
         /*
          * See do_swap_page(): PageWriteback() would be problematic.
          * However, we do a wait_on_page_writeback() just before this
          * call and have the page locked.
          */
         VM_BUG_ON_PAGE(PageWriteback(page), page);
         if (pte_swp_exclusive(*pte))
             rmap_flags |= RMAP_EXCLUSIVE;
 
         page_add_anon_rmap(page, vma, addr, rmap_flags);
     } else { /* ksm created a completely new copy */
         page_add_new_anon_rmap(page, vma, addr);
         lru_cache_add_inactive_or_unevictable(page, vma);
     }
     new_pte = pte_mkold(mk_pte(page, vma->vm_page_prot));
     if (pte_swp_soft_dirty(*pte))
         new_pte = pte_mksoft_dirty(new_pte);
     if (pte_swp_uffd_wp(*pte))
         new_pte = pte_mkuffd_wp(new_pte);
     set_pte_at(vma->vm_mm, addr, pte, new_pte);
     swap_free(entry);
 out:
     pte_unmap_unlock(pte, ptl);
     if (page != swapcache) {
         unlock_page(page);
         put_page(page);
     }
     return ret;
 }
 
 static int unuse_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
             unsigned long addr, unsigned long end,
             unsigned int type)
 {
     struct page *page;
     swp_entry_t entry;
     pte_t *pte;
     struct swap_info_struct *si;
     unsigned long offset;
     int ret = 0;
     volatile unsigned char *swap_map;
 
     si = swap_info[type];
     pte = pte_offset_map(pmd, addr);
     do {
         if (!is_swap_pte(*pte))
             continue;
 
         entry = pte_to_swp_entry(*pte);
         if (swp_type(entry) != type)
             continue;
 
         offset = swp_offset(entry);
         pte_unmap(pte);
         swap_map = &si->swap_map[offset];
         page = lookup_swap_cache(entry, vma, addr);
         if (!page) {
             struct vm_fault vmf = {
                 .vma = vma,
                 .address = addr,
                 .real_address = addr,
                 .pmd = pmd,
             };
 
             page = swapin_readahead(entry, GFP_HIGHUSER_MOVABLE,
                         &vmf);
         }
         if (!page) {
             if (*swap_map == 0 || *swap_map == SWAP_MAP_BAD)
                 goto try_next;
             return -ENOMEM;
         }
 
         lock_page(page);
         wait_on_page_writeback(page);
         ret = unuse_pte(vma, pmd, addr, entry, page);
         if (ret < 0) {
             unlock_page(page);
             put_page(page);
             goto out;
         }
 
         try_to_free_swap(page);
         unlock_page(page);
         put_page(page);
 try_next:
         pte = pte_offset_map(pmd, addr);
     } while (pte++, addr += PAGE_SIZE, addr != end);
     pte_unmap(pte - 1);
 
     ret = 0;
 out:
     return ret;
 }
 
 static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
                 unsigned long addr, unsigned long end,
                 unsigned int type)
 {
     pmd_t *pmd;
     unsigned long next;
     int ret;
 
     pmd = pmd_offset(pud, addr);
     do {
         cond_resched();
         next = pmd_addr_end(addr, end);
         if (pmd_none_or_trans_huge_or_clear_bad(pmd))
             continue;
         ret = unuse_pte_range(vma, pmd, addr, next, type);
         if (ret)
             return ret;
     } while (pmd++, addr = next, addr != end);
     return 0;
 }
 
 static inline int unuse_pud_range(struct vm_area_struct *vma, p4d_t *p4d,
                 unsigned long addr, unsigned long end,
                 unsigned int type)
 {
     pud_t *pud;
     unsigned long next;
     int ret;
 
     pud = pud_offset(p4d, addr);
     do {
         next = pud_addr_end(addr, end);
         if (pud_none_or_clear_bad(pud))
             continue;
         ret = unuse_pmd_range(vma, pud, addr, next, type);
         if (ret)
             return ret;
     } while (pud++, addr = next, addr != end);
     return 0;
 }
 
 static inline int unuse_p4d_range(struct vm_area_struct *vma, pgd_t *pgd,
                 unsigned long addr, unsigned long end,
                 unsigned int type)
 {
     p4d_t *p4d;
     unsigned long next;
     int ret;
 
     p4d = p4d_offset(pgd, addr);
     do {
         next = p4d_addr_end(addr, end);
         if (p4d_none_or_clear_bad(p4d))
             continue;
         ret = unuse_pud_range(vma, p4d, addr, next, type);
         if (ret)
             return ret;
     } while (p4d++, addr = next, addr != end);
     return 0;
 }
 
 static int unuse_vma(struct vm_area_struct *vma, unsigned int type)
 {
     pgd_t *pgd;
     unsigned long addr, end, next;
     int ret;
 
     addr = vma->vm_start;
     end = vma->vm_end;
 
     pgd = pgd_offset(vma->vm_mm, addr);
     do {
         next = pgd_addr_end(addr, end);
         if (pgd_none_or_clear_bad(pgd))
             continue;
         ret = unuse_p4d_range(vma, pgd, addr, next, type);
         if (ret)
             return ret;
     } while (pgd++, addr = next, addr != end);
     return 0;
 }
 
 static int unuse_mm(struct mm_struct *mm, unsigned int type)
 {
     struct vm_area_struct *vma;
     int ret = 0;
 
     mmap_read_lock(mm);
     for (vma = mm->mmap; vma; vma = vma->vm_next) {
         if (vma->anon_vma) {
             ret = unuse_vma(vma, type);
             if (ret)
                 break;
         }
         cond_resched();
     }
     mmap_read_unlock(mm);
     return ret;
 }
 
 /*
  * Scan swap_map from current position to next entry still in use.
  * Return 0 if there are no inuse entries after prev till end of
  * the map.
  */
 static unsigned int find_next_to_unuse(struct swap_info_struct *si,
                     unsigned int prev)
 {
     unsigned int i;
     unsigned char count;
 
     /*
      * No need for swap_lock here: we're just looking
      * for whether an entry is in use, not modifying it; false
      * hits are okay, and sys_swapoff() has already prevented new
      * allocations from this area (while holding swap_lock).
      */
     for (i = prev + 1; i < si->max; i++) {
         count = READ_ONCE(si->swap_map[i]);
         if (count && swap_count(count) != SWAP_MAP_BAD)
             break;
         if ((i % LATENCY_LIMIT) == 0)
             cond_resched();
     }
 
     if (i == si->max)
         i = 0;
 
     return i;
 }
 
 static int try_to_unuse(unsigned int type)
 {
     struct mm_struct *prev_mm;
     struct mm_struct *mm;
     struct list_head *p;
     int retval = 0;
     struct swap_info_struct *si = swap_info[type];
     struct page *page;
     swp_entry_t entry;
     unsigned int i;
 
     if (!READ_ONCE(si->inuse_pages))
         return 0;
 
 retry:
     retval = shmem_unuse(type);
     if (retval)
         return retval;
 
     prev_mm = &init_mm;
     mmget(prev_mm);
 
     spin_lock(&mmlist_lock);
     p = &init_mm.mmlist;
     while (READ_ONCE(si->inuse_pages) &&
            !signal_pending(current) &&
            (p = p->next) != &init_mm.mmlist) {
 
         mm = list_entry(p, struct mm_struct, mmlist);
         if (!mmget_not_zero(mm))
             continue;
         spin_unlock(&mmlist_lock);
         mmput(prev_mm);
         prev_mm = mm;
         retval = unuse_mm(mm, type);
         if (retval) {
             mmput(prev_mm);
             return retval;
         }
 
         /*
          * Make sure that we aren't completely killing
          * interactive performance.
          */
         cond_resched();
         spin_lock(&mmlist_lock);
     }
     spin_unlock(&mmlist_lock);
 
     mmput(prev_mm);
 
     i = 0;
     while (READ_ONCE(si->inuse_pages) &&
            !signal_pending(current) &&
            (i = find_next_to_unuse(si, i)) != 0) {
 
         entry = swp_entry(type, i);
         page = find_get_page(swap_address_space(entry), i);
         if (!page)
             continue;
 
         /*
          * It is conceivable that a racing task removed this page from
          * swap cache just before we acquired the page lock. The page
          * might even be back in swap cache on another swap area. But
          * that is okay, try_to_free_swap() only removes stale pages.
          */
         lock_page(page);
         wait_on_page_writeback(page);
         try_to_free_swap(page);
         unlock_page(page);
         put_page(page);
     }
 
     /*
      * Lets check again to see if there are still swap entries in the map.
      * If yes, we would need to do retry the unuse logic again.
      * Under global memory pressure, swap entries can be reinserted back
      * into process space after the mmlist loop above passes over them.
      *
      * Limit the number of retries? No: when mmget_not_zero()
      * above fails, that mm is likely to be freeing swap from
      * exit_mmap(), which proceeds at its own independent pace;
      * and even shmem_writepage() could have been preempted after
      * folio_alloc_swap(), temporarily hiding that swap.  It's easy
      * and robust (though cpu-intensive) just to keep retrying.
      */
     if (READ_ONCE(si->inuse_pages)) {
         if (!signal_pending(current))
             goto retry;
         return -EINTR;
     }
 
     return 0;
 }
 
 /*
  * After a successful try_to_unuse, if no swap is now in use, we know
  * we can empty the mmlist.  swap_lock must be held on entry and exit.
  * Note that mmlist_lock nests inside swap_lock, and an mm must be
  * added to the mmlist just after page_duplicate - before would be racy.
  */
 static void drain_mmlist(void)
 {
     struct list_head *p, *next;
     unsigned int type;
 
     for (type = 0; type < nr_swapfiles; type++)
         if (swap_info[type]->inuse_pages)
             return;
     spin_lock(&mmlist_lock);
     list_for_each_safe(p, next, &init_mm.mmlist)
         list_del_init(p);
     spin_unlock(&mmlist_lock);
 }
 
 /*
  * Free all of a swapdev's extent information
  */
 static void destroy_swap_extents(struct swap_info_struct *sis)
 {
     while (!RB_EMPTY_ROOT(&sis->swap_extent_root)) {
         struct rb_node *rb = sis->swap_extent_root.rb_node;
         struct swap_extent *se = rb_entry(rb, struct swap_extent, rb_node);
 
         rb_erase(rb, &sis->swap_extent_root);
         kfree(se);
     }
 
     if (sis->flags & SWP_ACTIVATED) {
         struct file *swap_file = sis->swap_file;
         struct address_space *mapping = swap_file->f_mapping;
 
         sis->flags &= ~SWP_ACTIVATED;
         if (mapping->a_ops->swap_deactivate)
             mapping->a_ops->swap_deactivate(swap_file);
     }
 }
 
 /*
  * Add a block range (and the corresponding page range) into this swapdev's
  * extent tree.
  *
  * This function rather assumes that it is called in ascending page order.
  */
 int
 add_swap_extent(struct swap_info_struct *sis, unsigned long start_page,
         unsigned long nr_pages, sector_t start_block)
 {
     struct rb_node **link = &sis->swap_extent_root.rb_node, *parent = NULL;
     struct swap_extent *se;
     struct swap_extent *new_se;
 
     /*
      * place the new node at the right most since the
      * function is called in ascending page order.
      */
     while (*link) {
         parent = *link;
         link = &parent->rb_right;
     }
 
     if (parent) {
         se = rb_entry(parent, struct swap_extent, rb_node);
         BUG_ON(se->start_page + se->nr_pages != start_page);
         if (se->start_block + se->nr_pages == start_block) {
             /* Merge it */
             se->nr_pages += nr_pages;
             return 0;
         }
     }
 
     /* No merge, insert a new extent. */
     new_se = kmalloc(sizeof(*se), GFP_KERNEL);
     if (new_se == NULL)
         return -ENOMEM;
     new_se->start_page = start_page;
     new_se->nr_pages = nr_pages;
     new_se->start_block = start_block;
 
     rb_link_node(&new_se->rb_node, parent, link);
     rb_insert_color(&new_se->rb_node, &sis->swap_extent_root);
     return 1;
 }
 EXPORT_SYMBOL_GPL(add_swap_extent);
 
 /*
  * A `swap extent' is a simple thing which maps a contiguous range of pages
  * onto a contiguous range of disk blocks.  A rbtree of swap extents is
  * built at swapon time and is then used at swap_writepage/swap_readpage
  * time for locating where on disk a page belongs.
  *
  * If the swapfile is an S_ISBLK block device, a single extent is installed.
  * This is done so that the main operating code can treat S_ISBLK and S_ISREG
  * swap files identically.
  *
  * Whether the swapdev is an S_ISREG file or an S_ISBLK blockdev, the swap
  * extent rbtree operates in PAGE_SIZE disk blocks.  Both S_ISREG and S_ISBLK
  * swapfiles are handled *identically* after swapon time.
  *
  * For S_ISREG swapfiles, setup_swap_extents() will walk all the file's blocks
  * and will parse them into a rbtree, in PAGE_SIZE chunks.  If some stray
  * blocks are found which do not fall within the PAGE_SIZE alignment
  * requirements, they are simply tossed out - we will never use those blocks
  * for swapping.
  *
  * For all swap devices we set S_SWAPFILE across the life of the swapon.  This
  * prevents users from writing to the swap device, which will corrupt memory.
  *
  * The amount of disk space which a single swap extent represents varies.
  * Typically it is in the 1-4 megabyte range.  So we can have hundreds of
  * extents in the rbtree. - akpm.
  */
 static int setup_swap_extents(struct swap_info_struct *sis, sector_t *span)
 {
     struct file *swap_file = sis->swap_file;
     struct address_space *mapping = swap_file->f_mapping;
     struct inode *inode = mapping->host;
     int ret;
 
     if (S_ISBLK(inode->i_mode)) {
         ret = add_swap_extent(sis, 0, sis->max, 0);
         *span = sis->pages;
         return ret;
     }
 
     if (mapping->a_ops->swap_activate) {
         ret = mapping->a_ops->swap_activate(sis, swap_file, span);
         if (ret < 0)
             return ret;
         sis->flags |= SWP_ACTIVATED;
         if ((sis->flags & SWP_FS_OPS) &&
             sio_pool_init() != 0) {
             destroy_swap_extents(sis);
             return -ENOMEM;
         }
         return ret;
     }
 
     return generic_swapfile_activate(sis, swap_file, span);
 }
 
 static int swap_node(struct swap_info_struct *p)
 {
     struct block_device *bdev;
 
     if (p->bdev)
         bdev = p->bdev;
     else
         bdev = p->swap_file->f_inode->i_sb->s_bdev;
 
     return bdev ? bdev->bd_disk->node_id : NUMA_NO_NODE;
 }
 
 static void setup_swap_info(struct swap_info_struct *p, int prio,
                 unsigned char *swap_map,
                 struct swap_cluster_info *cluster_info)
 {
     int i;
 
     if (prio >= 0)
         p->prio = prio;
     else
         p->prio = --least_priority;
     /*
      * the plist prio is negated because plist ordering is
      * low-to-high, while swap ordering is high-to-low
      */
     p->list.prio = -p->prio;
     for_each_node(i) {
         if (p->prio >= 0)
             p->avail_lists[i].prio = -p->prio;
         else {
             if (swap_node(p) == i)
                 p->avail_lists[i].prio = 1;
             else
                 p->avail_lists[i].prio = -p->prio;
         }
     }
     p->swap_map = swap_map;
     p->cluster_info = cluster_info;
 }
 
 static void _enable_swap_info(struct swap_info_struct *p)
 {
     p->flags |= SWP_WRITEOK;
     atomic_long_add(p->pages, &nr_swap_pages);
     total_swap_pages += p->pages;
 
     assert_spin_locked(&swap_lock);
     /*
      * both lists are plists, and thus priority ordered.
      * swap_active_head needs to be priority ordered for swapoff(),
      * which on removal of any swap_info_struct with an auto-assigned
      * (i.e. negative) priority increments the auto-assigned priority
      * of any lower-priority swap_info_structs.
      * swap_avail_head needs to be priority ordered for folio_alloc_swap(),
      * which allocates swap pages from the highest available priority
      * swap_info_struct.
      */
     plist_add(&p->list, &swap_active_head);
     add_to_avail_list(p);
 }
 
 static void enable_swap_info(struct swap_info_struct *p, int prio,
                 unsigned char *swap_map,
                 struct swap_cluster_info *cluster_info,
                 unsigned long *frontswap_map)
 {
     if (IS_ENABLED(CONFIG_FRONTSWAP))
         frontswap_init(p->type, frontswap_map);
     spin_lock(&swap_lock);
     spin_lock(&p->lock);
     setup_swap_info(p, prio, swap_map, cluster_info);
     spin_unlock(&p->lock);
     spin_unlock(&swap_lock);
     /*
      * Finished initializing swap device, now it's safe to reference it.
      */
     percpu_ref_resurrect(&p->users);
     spin_lock(&swap_lock);
     spin_lock(&p->lock);
     _enable_swap_info(p);
     spin_unlock(&p->lock);
     spin_unlock(&swap_lock);
 }
 
 static void reinsert_swap_info(struct swap_info_struct *p)
 {
     spin_lock(&swap_lock);
     spin_lock(&p->lock);
     setup_swap_info(p, p->prio, p->swap_map, p->cluster_info);
     _enable_swap_info(p);
     spin_unlock(&p->lock);
     spin_unlock(&swap_lock);
 }
 
 bool has_usable_swap(void)
 {
     bool ret = true;
 
     spin_lock(&swap_lock);
     if (plist_head_empty(&swap_active_head))
         ret = false;
     spin_unlock(&swap_lock);
     return ret;
 }
 
 SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 {
     struct swap_info_struct *p = NULL;
     unsigned char *swap_map;
     struct swap_cluster_info *cluster_info;
     unsigned long *frontswap_map;
     struct file *swap_file, *victim;
     struct address_space *mapping;
     struct inode *inode;
     struct filename *pathname;
     int err, found = 0;
     unsigned int old_block_size;
 
     if (!capable(CAP_SYS_ADMIN))
         return -EPERM;
 
     BUG_ON(!current->mm);
 
     pathname = getname(specialfile);
     if (IS_ERR(pathname))
         return PTR_ERR(pathname);
 
     victim = file_open_name(pathname, O_RDWR|O_LARGEFILE, 0);
     err = PTR_ERR(victim);
     if (IS_ERR(victim))
         goto out;
 
     mapping = victim->f_mapping;
     spin_lock(&swap_lock);
     plist_for_each_entry(p, &swap_active_head, list) {
         if (p->flags & SWP_WRITEOK) {
             if (p->swap_file->f_mapping == mapping) {
                 found = 1;
                 break;
             }
         }
     }
     if (!found) {
         err = -EINVAL;
         spin_unlock(&swap_lock);
         goto out_dput;
     }
     if (!security_vm_enough_memory_mm(current->mm, p->pages))
         vm_unacct_memory(p->pages);
     else {
         err = -ENOMEM;
         spin_unlock(&swap_lock);
         goto out_dput;
     }
     del_from_avail_list(p);
     spin_lock(&p->lock);
     if (p->prio < 0) {
         struct swap_info_struct *si = p;
         int nid;
 
         plist_for_each_entry_continue(si, &swap_active_head, list) {
             si->prio++;
             si->list.prio--;
             for_each_node(nid) {
                 if (si->avail_lists[nid].prio != 1)
                     si->avail_lists[nid].prio--;
             }
         }
         least_priority++;
     }
     plist_del(&p->list, &swap_active_head);
     atomic_long_sub(p->pages, &nr_swap_pages);
     total_swap_pages -= p->pages;
     p->flags &= ~SWP_WRITEOK;
     spin_unlock(&p->lock);
     spin_unlock(&swap_lock);
 
     disable_swap_slots_cache_lock();
 
     set_current_oom_origin();
     err = try_to_unuse(p->type);
     clear_current_oom_origin();
 
     if (err) {
         /* re-insert swap space back into swap_list */
         reinsert_swap_info(p);
         reenable_swap_slots_cache_unlock();
         goto out_dput;
     }
 
     reenable_swap_slots_cache_unlock();
 
     /*
      * Wait for swap operations protected by get/put_swap_device()
      * to complete.
      *
      * We need synchronize_rcu() here to protect the accessing to
      * the swap cache data structure.
      */
     percpu_ref_kill(&p->users);
     synchronize_rcu();
     wait_for_completion(&p->comp);
 
     flush_work(&p->discard_work);
 
     destroy_swap_extents(p);
     if (p->flags & SWP_CONTINUED)
         free_swap_count_continuations(p);
 
     if (!p->bdev || !bdev_nonrot(p->bdev))
         atomic_dec(&nr_rotate_swap);
 
     mutex_lock(&swapon_mutex);
     spin_lock(&swap_lock);
     spin_lock(&p->lock);
     drain_mmlist();
 
     /* wait for anyone still in scan_swap_map_slots */
     p->highest_bit = 0;     /* cuts scans short */
     while (p->flags >= SWP_SCANNING) {
         spin_unlock(&p->lock);
         spin_unlock(&swap_lock);
         schedule_timeout_uninterruptible(1);
         spin_lock(&swap_lock);
         spin_lock(&p->lock);
     }
 
     swap_file = p->swap_file;
     old_block_size = p->old_block_size;
     p->swap_file = NULL;
     p->max = 0;
     swap_map = p->swap_map;
     p->swap_map = NULL;
     cluster_info = p->cluster_info;
     p->cluster_info = NULL;
     frontswap_map = frontswap_map_get(p);
     spin_unlock(&p->lock);
     spin_unlock(&swap_lock);
     arch_swap_invalidate_area(p->type);
     frontswap_invalidate_area(p->type);
     frontswap_map_set(p, NULL);
     mutex_unlock(&swapon_mutex);
     free_percpu(p->percpu_cluster);
     p->percpu_cluster = NULL;
     free_percpu(p->cluster_next_cpu);
     p->cluster_next_cpu = NULL;
     vfree(swap_map);
     kvfree(cluster_info);
     kvfree(frontswap_map);
     /* Destroy swap account information */
     swap_cgroup_swapoff(p->type);
     exit_swap_address_space(p->type);
 
     inode = mapping->host;
     if (S_ISBLK(inode->i_mode)) {
         struct block_device *bdev = I_BDEV(inode);
 
         set_blocksize(bdev, old_block_size);
         blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
     }
 
     inode_lock(inode);
     inode->i_flags &= ~S_SWAPFILE;
     inode_unlock(inode);
     filp_close(swap_file, NULL);
 
     /*
      * Clear the SWP_USED flag after all resources are freed so that swapon
      * can reuse this swap_info in alloc_swap_info() safely.  It is ok to
      * not hold p->lock after we cleared its SWP_WRITEOK.
      */
     spin_lock(&swap_lock);
     p->flags = 0;
     spin_unlock(&swap_lock);
 
     err = 0;
     atomic_inc(&proc_poll_event);
     wake_up_interruptible(&proc_poll_wait);
 
 out_dput:
     filp_close(victim, NULL);
 out:
     putname(pathname);
     return err;
 }
 
 #ifdef CONFIG_PROC_FS
 static __poll_t swaps_poll(struct file *file, poll_table *wait)
 {
     struct seq_file *seq = file->private_data;
 
     poll_wait(file, &proc_poll_wait, wait);
 
     if (seq->poll_event != atomic_read(&proc_poll_event)) {
         seq->poll_event = atomic_read(&proc_poll_event);
         return EPOLLIN | EPOLLRDNORM | EPOLLERR | EPOLLPRI;
     }
 
     return EPOLLIN | EPOLLRDNORM;
 }
 
 /* iterator */
 static void *swap_start(struct seq_file *swap, loff_t *pos)
 {
     struct swap_info_struct *si;
     int type;
     loff_t l = *pos;
 
     mutex_lock(&swapon_mutex);
 
     if (!l)
         return SEQ_START_TOKEN;
 
     for (type = 0; (si = swap_type_to_swap_info(type)); type++) {
         if (!(si->flags & SWP_USED) || !si->swap_map)
             continue;
         if (!--l)
             return si;
     }
 
     return NULL;
 }
 
 static void *swap_next(struct seq_file *swap, void *v, loff_t *pos)
 {
     struct swap_info_struct *si = v;
     int type;
 
     if (v == SEQ_START_TOKEN)
         type = 0;
     else
         type = si->type + 1;
 
     ++(*pos);
     for (; (si = swap_type_to_swap_info(type)); type++) {
         if (!(si->flags & SWP_USED) || !si->swap_map)
             continue;
         return si;
     }
 
     return NULL;
 }
 
 static void swap_stop(struct seq_file *swap, void *v)
 {
     mutex_unlock(&swapon_mutex);
 }
 
 static int swap_show(struct seq_file *swap, void *v)
 {
     struct swap_info_struct *si = v;
     struct file *file;
     int len;
     unsigned long bytes, inuse;
 
     if (si == SEQ_START_TOKEN) {
         seq_puts(swap, "Filename\t\t\t\tType\t\tSize\t\tUsed\t\tPriority\n");
         return 0;
     }
 
     bytes = si->pages << (PAGE_SHIFT - 10);
     inuse = READ_ONCE(si->inuse_pages) << (PAGE_SHIFT - 10);
 
     file = si->swap_file;
     len = seq_file_path(swap, file, " \t\n\\");
     seq_printf(swap, "%*s%s\t%lu\t%s%lu\t%s%d\n",
             len < 40 ? 40 - len : 1, " ",
             S_ISBLK(file_inode(file)->i_mode) ?
                 "partition" : "file\t",
             bytes, bytes < 10000000 ? "\t" : "",
             inuse, inuse < 10000000 ? "\t" : "",
             si->prio);
     return 0;
 }
 
 static const struct seq_operations swaps_op = {
     .start =    swap_start,
     .next =     swap_next,
     .stop =     swap_stop,
     .show =     swap_show
 };
 
 static int swaps_open(struct inode *inode, struct file *file)
 {
     struct seq_file *seq;
     int ret;
 
     ret = seq_open(file, &swaps_op);
     if (ret)
         return ret;
 
     seq = file->private_data;
     seq->poll_event = atomic_read(&proc_poll_event);
     return 0;
 }
 
 static const struct proc_ops swaps_proc_ops = {
     .proc_flags = PROC_ENTRY_PERMANENT,
     .proc_open  = swaps_open,
     .proc_read  = seq_read,
     .proc_lseek = seq_lseek,
     .proc_release   = seq_release,
     .proc_poll  = swaps_poll,
 };
 
 static int __init procswaps_init(void)
 {
     proc_create("swaps", 0, NULL, &swaps_proc_ops);
     return 0;
 }
 __initcall(procswaps_init);
 #endif /* CONFIG_PROC_FS */
 
 #ifdef MAX_SWAPFILES_CHECK
 static int __init max_swapfiles_check(void)
 {
     MAX_SWAPFILES_CHECK();
     return 0;
 }
 late_initcall(max_swapfiles_check);
 #endif
 
 static struct swap_info_struct *alloc_swap_info(void)
 {
     struct swap_info_struct *p;
     struct swap_info_struct *defer = NULL;
     unsigned int type;
     int i;
 
     p = kvzalloc(struct_size(p, avail_lists, nr_node_ids), GFP_KERNEL);
     if (!p)
         return ERR_PTR(-ENOMEM);
 
     if (percpu_ref_init(&p->users, swap_users_ref_free,
                 PERCPU_REF_INIT_DEAD, GFP_KERNEL)) {
         kvfree(p);
         return ERR_PTR(-ENOMEM);
     }
 
     spin_lock(&swap_lock);
     for (type = 0; type < nr_swapfiles; type++) {
         if (!(swap_info[type]->flags & SWP_USED))
             break;
     }
     if (type >= MAX_SWAPFILES) {
         spin_unlock(&swap_lock);
         percpu_ref_exit(&p->users);
         kvfree(p);
         return ERR_PTR(-EPERM);
     }
     if (type >= nr_swapfiles) {
         p->type = type;
         /*
          * Publish the swap_info_struct after initializing it.
          * Note that kvzalloc() above zeroes all its fields.
          */
         smp_store_release(&swap_info[type], p); /* rcu_assign_pointer() */
         nr_swapfiles++;
     } else {
         defer = p;
         p = swap_info[type];
         /*
          * Do not memset this entry: a racing procfs swap_next()
          * would be relying on p->type to remain valid.
          */
     }
     p->swap_extent_root = RB_ROOT;
     plist_node_init(&p->list, 0);
     for_each_node(i)
         plist_node_init(&p->avail_lists[i], 0);
     p->flags = SWP_USED;
     spin_unlock(&swap_lock);
     if (defer) {
         percpu_ref_exit(&defer->users);
         kvfree(defer);
     }
     spin_lock_init(&p->lock);
     spin_lock_init(&p->cont_lock);
     init_completion(&p->comp);
 
     return p;
 }
 
 static int claim_swapfile(struct swap_info_struct *p, struct inode *inode)
 {
     int error;
 
     if (S_ISBLK(inode->i_mode)) {
         p->bdev = blkdev_get_by_dev(inode->i_rdev,
                    FMODE_READ | FMODE_WRITE | FMODE_EXCL, p);
         if (IS_ERR(p->bdev)) {
             error = PTR_ERR(p->bdev);
             p->bdev = NULL;
             return error;
         }
         p->old_block_size = block_size(p->bdev);
         error = set_blocksize(p->bdev, PAGE_SIZE);
         if (error < 0)
             return error;
         /*
          * Zoned block devices contain zones that have a sequential
          * write only restriction.  Hence zoned block devices are not
          * suitable for swapping.  Disallow them here.
          */
         if (bdev_is_zoned(p->bdev))
             return -EINVAL;
         p->flags |= SWP_BLKDEV;
     } else if (S_ISREG(inode->i_mode)) {
         p->bdev = inode->i_sb->s_bdev;
     }
 
     return 0;
 }
 
 
 /*
  * Find out how many pages are allowed for a single swap device. There
  * are two limiting factors:
  * 1) the number of bits for the swap offset in the swp_entry_t type, and
  * 2) the number of bits in the swap pte, as defined by the different
  * architectures.
  *
  * In order to find the largest possible bit mask, a swap entry with
  * swap type 0 and swap offset ~0UL is created, encoded to a swap pte,
  * decoded to a swp_entry_t again, and finally the swap offset is
  * extracted.
  *
  * This will mask all the bits from the initial ~0UL mask that can't
  * be encoded in either the swp_entry_t or the architecture definition
  * of a swap pte.
  */
 unsigned long generic_max_swapfile_size(void)
 {
     return swp_offset(pte_to_swp_entry(
             swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
 }
 
 /* Can be overridden by an architecture for additional checks. */
 __weak unsigned long max_swapfile_size(void)
 {
     return generic_max_swapfile_size();
 }
 
 static unsigned long read_swap_header(struct swap_info_struct *p,
                     union swap_header *swap_header,
                     struct inode *inode)
 {
     int i;
     unsigned long maxpages;
     unsigned long swapfilepages;
     unsigned long last_page;
 
     if (memcmp("SWAPSPACE2", swap_header->magic.magic, 10)) {
         pr_err("Unable to find swap-space signature\n");
         return 0;
     }
 
     /* swap partition endianness hack... */
     if (swab32(swap_header->info.version) == 1) {
         swab32s(&swap_header->info.version);
         swab32s(&swap_header->info.last_page);
         swab32s(&swap_header->info.nr_badpages);
         if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
             return 0;
         for (i = 0; i < swap_header->info.nr_badpages; i++)
             swab32s(&swap_header->info.badpages[i]);
     }
     /* Check the swap header's sub-version */
     if (swap_header->info.version != 1) {
         pr_warn("Unable to handle swap header version %d\n",
             swap_header->info.version);
         return 0;
     }
 
     p->lowest_bit  = 1;
     p->cluster_next = 1;
     p->cluster_nr = 0;
 
     maxpages = max_swapfile_size();
     last_page = swap_header->info.last_page;
     if (!last_page) {
         pr_warn("Empty swap-file\n");
         return 0;
     }
     if (last_page > maxpages) {
         pr_warn("Truncating oversized swap area, only using %luk out of %luk\n",
             maxpages << (PAGE_SHIFT - 10),
             last_page << (PAGE_SHIFT - 10));
     }
     if (maxpages > last_page) {
         maxpages = last_page + 1;
         /* p->max is an unsigned int: don't overflow it */
         if ((unsigned int)maxpages == 0)
             maxpages = UINT_MAX;
     }
     p->highest_bit = maxpages - 1;
 
     if (!maxpages)
         return 0;
     swapfilepages = i_size_read(inode) >> PAGE_SHIFT;
     if (swapfilepages && maxpages > swapfilepages) {
         pr_warn("Swap area shorter than signature indicates\n");
         return 0;
     }
     if (swap_header->info.nr_badpages && S_ISREG(inode->i_mode))
         return 0;
     if (swap_header->info.nr_badpages > MAX_SWAP_BADPAGES)
         return 0;
 
     return maxpages;
 }
 
 #define SWAP_CLUSTER_INFO_COLS                      \
     DIV_ROUND_UP(L1_CACHE_BYTES, sizeof(struct swap_cluster_info))
 #define SWAP_CLUSTER_SPACE_COLS                     \
     DIV_ROUND_UP(SWAP_ADDRESS_SPACE_PAGES, SWAPFILE_CLUSTER)
 #define SWAP_CLUSTER_COLS                       \
     max_t(unsigned int, SWAP_CLUSTER_INFO_COLS, SWAP_CLUSTER_SPACE_COLS)
 
 static int setup_swap_map_and_extents(struct swap_info_struct *p,
                     union swap_header *swap_header,
                     unsigned char *swap_map,
                     struct swap_cluster_info *cluster_info,
                     unsigned long maxpages,
                     sector_t *span)
 {
     unsigned int j, k;
     unsigned int nr_good_pages;
     int nr_extents;
     unsigned long nr_clusters = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
     unsigned long col = p->cluster_next / SWAPFILE_CLUSTER % SWAP_CLUSTER_COLS;
     unsigned long i, idx;
 
     nr_good_pages = maxpages - 1;   /* omit header page */
 
     cluster_list_init(&p->free_clusters);
     cluster_list_init(&p->discard_clusters);
 
     for (i = 0; i < swap_header->info.nr_badpages; i++) {
         unsigned int page_nr = swap_header->info.badpages[i];
         if (page_nr == 0 || page_nr > swap_header->info.last_page)
             return -EINVAL;
         if (page_nr < maxpages) {
             swap_map[page_nr] = SWAP_MAP_BAD;
             nr_good_pages--;
             /*
              * Haven't marked the cluster free yet, no list
              * operation involved
              */
             inc_cluster_info_page(p, cluster_info, page_nr);
         }
     }
 
     /* Haven't marked the cluster free yet, no list operation involved */
     for (i = maxpages; i < round_up(maxpages, SWAPFILE_CLUSTER); i++)
         inc_cluster_info_page(p, cluster_info, i);
 
     if (nr_good_pages) {
         swap_map[0] = SWAP_MAP_BAD;
         /*
          * Not mark the cluster free yet, no list
          * operation involved
          */
         inc_cluster_info_page(p, cluster_info, 0);
         p->max = maxpages;
         p->pages = nr_good_pages;
         nr_extents = setup_swap_extents(p, span);
         if (nr_extents < 0)
             return nr_extents;
         nr_good_pages = p->pages;
     }
     if (!nr_good_pages) {
         pr_warn("Empty swap-file\n");
         return -EINVAL;
     }
 
     if (!cluster_info)
         return nr_extents;
 
 
     /*
      * Reduce false cache line sharing between cluster_info and
      * sharing same address space.
      */
     for (k = 0; k < SWAP_CLUSTER_COLS; k++) {
         j = (k + col) % SWAP_CLUSTER_COLS;
         for (i = 0; i < DIV_ROUND_UP(nr_clusters, SWAP_CLUSTER_COLS); i++) {
             idx = i * SWAP_CLUSTER_COLS + j;
             if (idx >= nr_clusters)
                 continue;
             if (cluster_count(&cluster_info[idx]))
                 continue;
             cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE);
             cluster_list_add_tail(&p->free_clusters, cluster_info,
                           idx);
         }
     }
     return nr_extents;
 }
 
 SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 {
     struct swap_info_struct *p;
     struct filename *name;
     struct file *swap_file = NULL;
     struct address_space *mapping;
     struct dentry *dentry;
     int prio;
     int error;
     union swap_header *swap_header;
     int nr_extents;
     sector_t span;
     unsigned long maxpages;
     unsigned char *swap_map = NULL;
     struct swap_cluster_info *cluster_info = NULL;
     unsigned long *frontswap_map = NULL;
     struct page *page = NULL;
     struct inode *inode = NULL;
     bool inced_nr_rotate_swap = false;
 
     if (swap_flags & ~SWAP_FLAGS_VALID)
         return -EINVAL;
 
     if (!capable(CAP_SYS_ADMIN))
         return -EPERM;
 
     if (!swap_avail_heads)
         return -ENOMEM;
 
     p = alloc_swap_info();
     if (IS_ERR(p))
         return PTR_ERR(p);
 
     INIT_WORK(&p->discard_work, swap_discard_work);
 
     name = getname(specialfile);
     if (IS_ERR(name)) {
         error = PTR_ERR(name);
         name = NULL;
         goto bad_swap;
     }
     swap_file = file_open_name(name, O_RDWR|O_LARGEFILE, 0);
     if (IS_ERR(swap_file)) {
         error = PTR_ERR(swap_file);
         swap_file = NULL;
         goto bad_swap;
     }
 
     p->swap_file = swap_file;
     mapping = swap_file->f_mapping;
     dentry = swap_file->f_path.dentry;
     inode = mapping->host;
 
     error = claim_swapfile(p, inode);
     if (unlikely(error))
         goto bad_swap;
 
     inode_lock(inode);
     if (d_unlinked(dentry) || cant_mount(dentry)) {
         error = -ENOENT;
         goto bad_swap_unlock_inode;
     }
     if (IS_SWAPFILE(inode)) {
         error = -EBUSY;
         goto bad_swap_unlock_inode;
     }
 
     /*
      * Read the swap header.
      */
     if (!mapping->a_ops->read_folio) {
         error = -EINVAL;
         goto bad_swap_unlock_inode;
     }
     page = read_mapping_page(mapping, 0, swap_file);
     if (IS_ERR(page)) {
         error = PTR_ERR(page);
         goto bad_swap_unlock_inode;
     }
     swap_header = kmap(page);
 
     maxpages = read_swap_header(p, swap_header, inode);
     if (unlikely(!maxpages)) {
         error = -EINVAL;
         goto bad_swap_unlock_inode;
     }
 
     /* OK, set up the swap map and apply the bad block list */
     swap_map = vzalloc(maxpages);
     if (!swap_map) {
         error = -ENOMEM;
         goto bad_swap_unlock_inode;
     }
 
     if (p->bdev && bdev_stable_writes(p->bdev))
         p->flags |= SWP_STABLE_WRITES;
 
     if (p->bdev && p->bdev->bd_disk->fops->rw_page)
         p->flags |= SWP_SYNCHRONOUS_IO;
 
     if (p->bdev && bdev_nonrot(p->bdev)) {
         int cpu;
         unsigned long ci, nr_cluster;
 
         p->flags |= SWP_SOLIDSTATE;
         p->cluster_next_cpu = alloc_percpu(unsigned int);
         if (!p->cluster_next_cpu) {
             error = -ENOMEM;
             goto bad_swap_unlock_inode;
         }
         /*
          * select a random position to start with to help wear leveling
          * SSD
          */
         for_each_possible_cpu(cpu) {
             per_cpu(*p->cluster_next_cpu, cpu) =
                 1 + prandom_u32_max(p->highest_bit);
         }
         nr_cluster = DIV_ROUND_UP(maxpages, SWAPFILE_CLUSTER);
 
         cluster_info = kvcalloc(nr_cluster, sizeof(*cluster_info),
                     GFP_KERNEL);
         if (!cluster_info) {
             error = -ENOMEM;
             goto bad_swap_unlock_inode;
         }
 
         for (ci = 0; ci < nr_cluster; ci++)
             spin_lock_init(&((cluster_info + ci)->lock));
 
         p->percpu_cluster = alloc_percpu(struct percpu_cluster);
         if (!p->percpu_cluster) {
             error = -ENOMEM;
             goto bad_swap_unlock_inode;
         }
         for_each_possible_cpu(cpu) {
             struct percpu_cluster *cluster;
             cluster = per_cpu_ptr(p->percpu_cluster, cpu);
             cluster_set_null(&cluster->index);
         }
     } else {
         atomic_inc(&nr_rotate_swap);
         inced_nr_rotate_swap = true;
     }
 
     error = swap_cgroup_swapon(p->type, maxpages);
     if (error)
         goto bad_swap_unlock_inode;
 
     nr_extents = setup_swap_map_and_extents(p, swap_header, swap_map,
         cluster_info, maxpages, &span);
     if (unlikely(nr_extents < 0)) {
         error = nr_extents;
         goto bad_swap_unlock_inode;
     }
     /* frontswap enabled? set up bit-per-page map for frontswap */
     if (IS_ENABLED(CONFIG_FRONTSWAP))
         frontswap_map = kvcalloc(BITS_TO_LONGS(maxpages),
                      sizeof(long),
                      GFP_KERNEL);
 
     if ((swap_flags & SWAP_FLAG_DISCARD) &&
         p->bdev && bdev_max_discard_sectors(p->bdev)) {
         /*
          * When discard is enabled for swap with no particular
          * policy flagged, we set all swap discard flags here in
          * order to sustain backward compatibility with older
          * swapon(8) releases.
          */
         p->flags |= (SWP_DISCARDABLE | SWP_AREA_DISCARD |
                  SWP_PAGE_DISCARD);
 
         /*
          * By flagging sys_swapon, a sysadmin can tell us to
          * either do single-time area discards only, or to just
          * perform discards for released swap page-clusters.
          * Now it's time to adjust the p->flags accordingly.
          */
         if (swap_flags & SWAP_FLAG_DISCARD_ONCE)
             p->flags &= ~SWP_PAGE_DISCARD;
         else if (swap_flags & SWAP_FLAG_DISCARD_PAGES)
             p->flags &= ~SWP_AREA_DISCARD;
 
         /* issue a swapon-time discard if it's still required */
         if (p->flags & SWP_AREA_DISCARD) {
             int err = discard_swap(p);
             if (unlikely(err))
                 pr_err("swapon: discard_swap(%p): %d\n",
                     p, err);
         }
     }
 
     error = init_swap_address_space(p->type, maxpages);
     if (error)
         goto bad_swap_unlock_inode;
 
     /*
      * Flush any pending IO and dirty mappings before we start using this
      * swap device.
      */
     inode->i_flags |= S_SWAPFILE;
     error = inode_drain_writes(inode);
     if (error) {
         inode->i_flags &= ~S_SWAPFILE;
         goto free_swap_address_space;
     }
 
     mutex_lock(&swapon_mutex);
     prio = -1;
     if (swap_flags & SWAP_FLAG_PREFER)
         prio =
           (swap_flags & SWAP_FLAG_PRIO_MASK) >> SWAP_FLAG_PRIO_SHIFT;
     enable_swap_info(p, prio, swap_map, cluster_info, frontswap_map);
 
     pr_info("Adding %uk swap on %s.  Priority:%d extents:%d across:%lluk %s%s%s%s%s\n",
         p->pages<<(PAGE_SHIFT-10), name->name, p->prio,
         nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
         (p->flags & SWP_SOLIDSTATE) ? "SS" : "",
         (p->flags & SWP_DISCARDABLE) ? "D" : "",
         (p->flags & SWP_AREA_DISCARD) ? "s" : "",
         (p->flags & SWP_PAGE_DISCARD) ? "c" : "",
         (frontswap_map) ? "FS" : "");
 
     mutex_unlock(&swapon_mutex);
     atomic_inc(&proc_poll_event);
     wake_up_interruptible(&proc_poll_wait);
 
     error = 0;
     goto out;
 free_swap_address_space:
     exit_swap_address_space(p->type);
 bad_swap_unlock_inode:
     inode_unlock(inode);
 bad_swap:
     free_percpu(p->percpu_cluster);
     p->percpu_cluster = NULL;
     free_percpu(p->cluster_next_cpu);
     p->cluster_next_cpu = NULL;
     if (inode && S_ISBLK(inode->i_mode) && p->bdev) {
         set_blocksize(p->bdev, p->old_block_size);
         blkdev_put(p->bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
     }
     inode = NULL;
     destroy_swap_extents(p);
     swap_cgroup_swapoff(p->type);
     spin_lock(&swap_lock);
     p->swap_file = NULL;
     p->flags = 0;
     spin_unlock(&swap_lock);
     vfree(swap_map);
     kvfree(cluster_info);
     kvfree(frontswap_map);
     if (inced_nr_rotate_swap)
         atomic_dec(&nr_rotate_swap);
     if (swap_file)
         filp_close(swap_file, NULL);
 out:
     if (page && !IS_ERR(page)) {
         kunmap(page);
         put_page(page);
     }
     if (name)
         putname(name);
     if (inode)
         inode_unlock(inode);
     if (!error)
         enable_swap_slots_cache();
     return error;
 }
 
 void si_swapinfo(struct sysinfo *val)
 {
     unsigned int type;
     unsigned long nr_to_be_unused = 0;
 
     spin_lock(&swap_lock);
     for (type = 0; type < nr_swapfiles; type++) {
         struct swap_info_struct *si = swap_info[type];
 
         if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK))
             nr_to_be_unused += READ_ONCE(si->inuse_pages);
     }
     val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused;
     val->totalswap = total_swap_pages + nr_to_be_unused;
     spin_unlock(&swap_lock);
 }
 
 /*
  * Verify that a swap entry is valid and increment its swap map count.
  *
  * Returns error code in following case.
  * - success -> 0
  * - swp_entry is invalid -> EINVAL
  * - swp_entry is migration entry -> EINVAL
  * - swap-cache reference is requested but there is already one. -> EEXIST
  * - swap-cache reference is requested but the entry is not used. -> ENOENT
  * - swap-mapped reference requested but needs continued swap count. -> ENOMEM
  */
 static int __swap_duplicate(swp_entry_t entry, unsigned char usage)
 {
     struct swap_info_struct *p;
     struct swap_cluster_info *ci;
     unsigned long offset;
     unsigned char count;
     unsigned char has_cache;
     int err;
 
     p = get_swap_device(entry);
     if (!p)
         return -EINVAL;
 
     offset = swp_offset(entry);
     ci = lock_cluster_or_swap_info(p, offset);
 
     count = p->swap_map[offset];
 
     /*
      * swapin_readahead() doesn't check if a swap entry is valid, so the
      * swap entry could be SWAP_MAP_BAD. Check here with lock held.
      */
     if (unlikely(swap_count(count) == SWAP_MAP_BAD)) {
         err = -ENOENT;
         goto unlock_out;
     }
 
     has_cache = count & SWAP_HAS_CACHE;
     count &= ~SWAP_HAS_CACHE;
     err = 0;
 
     if (usage == SWAP_HAS_CACHE) {
 
         /* set SWAP_HAS_CACHE if there is no cache and entry is used */
         if (!has_cache && count)
             has_cache = SWAP_HAS_CACHE;
         else if (has_cache)     /* someone else added cache */
             err = -EEXIST;
         else                /* no users remaining */
             err = -ENOENT;
 
     } else if (count || has_cache) {
 
         if ((count & ~COUNT_CONTINUED) < SWAP_MAP_MAX)
             count += usage;
         else if ((count & ~COUNT_CONTINUED) > SWAP_MAP_MAX)
             err = -EINVAL;
         else if (swap_count_continued(p, offset, count))
             count = COUNT_CONTINUED;
         else
             err = -ENOMEM;
     } else
         err = -ENOENT;          /* unused swap entry */
 
     WRITE_ONCE(p->swap_map[offset], count | has_cache);
 
 unlock_out:
     unlock_cluster_or_swap_info(p, ci);
     put_swap_device(p);
     return err;
 }
 
 /*
  * Help swapoff by noting that swap entry belongs to shmem/tmpfs
  * (in which case its reference count is never incremented).
  */
 void swap_shmem_alloc(swp_entry_t entry)
 {
     __swap_duplicate(entry, SWAP_MAP_SHMEM);
 }
 
 /*
  * Increase reference count of swap entry by 1.
  * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
  * but could not be atomically allocated.  Returns 0, just as if it succeeded,
  * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
  * might occur if a page table entry has got corrupted.
  */
 int swap_duplicate(swp_entry_t entry)
 {
     int err = 0;
 
     while (!err && __swap_duplicate(entry, 1) == -ENOMEM)
         err = add_swap_count_continuation(entry, GFP_ATOMIC);
     return err;
 }
 
 /*
  * @entry: swap entry for which we allocate swap cache.
  *
  * Called when allocating swap cache for existing swap entry,
  * This can return error codes. Returns 0 at success.
  * -EEXIST means there is a swap cache.
  * Note: return code is different from swap_duplicate().
  */
 int swapcache_prepare(swp_entry_t entry)
 {
     return __swap_duplicate(entry, SWAP_HAS_CACHE);
 }
 
 struct swap_info_struct *swp_swap_info(swp_entry_t entry)
 {
     return swap_type_to_swap_info(swp_type(entry));
 }
 
 struct swap_info_struct *page_swap_info(struct page *page)
 {
     swp_entry_t entry = { .val = page_private(page) };
     return swp_swap_info(entry);
 }
 
 /*
  * out-of-line methods to avoid include hell.
  */
 struct address_space *swapcache_mapping(struct folio *folio)
 {
     return page_swap_info(&folio->page)->swap_file->f_mapping;
 }
 EXPORT_SYMBOL_GPL(swapcache_mapping);
 
 pgoff_t __page_file_index(struct page *page)
 {
     swp_entry_t swap = { .val = page_private(page) };
     return swp_offset(swap);
 }
 EXPORT_SYMBOL_GPL(__page_file_index);
 
 /*
  * add_swap_count_continuation - called when a swap count is duplicated
  * beyond SWAP_MAP_MAX, it allocates a new page and links that to the entry's
  * page of the original vmalloc'ed swap_map, to hold the continuation count
  * (for that entry and for its neighbouring PAGE_SIZE swap entries).  Called
  * again when count is duplicated beyond SWAP_MAP_MAX * SWAP_CONT_MAX, etc.
  *
  * These continuation pages are seldom referenced: the common paths all work
  * on the original swap_map, only referring to a continuation page when the
  * low "digit" of a count is incremented or decremented through SWAP_MAP_MAX.
  *
  * add_swap_count_continuation(, GFP_ATOMIC) can be called while holding
  * page table locks; if it fails, add_swap_count_continuation(, GFP_KERNEL)
  * can be called after dropping locks.
  */
 int add_swap_count_continuation(swp_entry_t entry, gfp_t gfp_mask)
 {
     struct swap_info_struct *si;
     struct swap_cluster_info *ci;
     struct page *head;
     struct page *page;
     struct page *list_page;
     pgoff_t offset;
     unsigned char count;
     int ret = 0;
 
     /*
      * When debugging, it's easier to use __GFP_ZERO here; but it's better
      * for latency not to zero a page while GFP_ATOMIC and holding locks.
      */
     page = alloc_page(gfp_mask | __GFP_HIGHMEM);
 
     si = get_swap_device(entry);
     if (!si) {
         /*
          * An acceptable race has occurred since the failing
          * __swap_duplicate(): the swap device may be swapoff
          */
         goto outer;
     }
     spin_lock(&si->lock);
 
     offset = swp_offset(entry);
 
     ci = lock_cluster(si, offset);
 
     count = swap_count(si->swap_map[offset]);
 
     if ((count & ~COUNT_CONTINUED) != SWAP_MAP_MAX) {
         /*
          * The higher the swap count, the more likely it is that tasks
          * will race to add swap count continuation: we need to avoid
          * over-provisioning.
          */
         goto out;
     }
 
     if (!page) {
         ret = -ENOMEM;
         goto out;
     }
 
     /*
      * We are fortunate that although vmalloc_to_page uses pte_offset_map,
      * no architecture is using highmem pages for kernel page tables: so it
      * will not corrupt the GFP_ATOMIC caller's atomic page table kmaps.
      */
     head = vmalloc_to_page(si->swap_map + offset);
     offset &= ~PAGE_MASK;
 
     spin_lock(&si->cont_lock);
     /*
      * Page allocation does not initialize the page's lru field,
      * but it does always reset its private field.
      */
     if (!page_private(head)) {
         BUG_ON(count & COUNT_CONTINUED);
         INIT_LIST_HEAD(&head->lru);
         set_page_private(head, SWP_CONTINUED);
         si->flags |= SWP_CONTINUED;
     }
 
     list_for_each_entry(list_page, &head->lru, lru) {
         unsigned char *map;
 
         /*
          * If the previous map said no continuation, but we've found
          * a continuation page, free our allocation and use this one.
          */
         if (!(count & COUNT_CONTINUED))
             goto out_unlock_cont;
 
         map = kmap_atomic(list_page) + offset;
         count = *map;
         kunmap_atomic(map);
 
         /*
          * If this continuation count now has some space in it,
          * free our allocation and use this one.
          */
         if ((count & ~COUNT_CONTINUED) != SWAP_CONT_MAX)
             goto out_unlock_cont;
     }
 
     list_add_tail(&page->lru, &head->lru);
     page = NULL;            /* now it's attached, don't free it */
 out_unlock_cont:
     spin_unlock(&si->cont_lock);
 out:
     unlock_cluster(ci);
     spin_unlock(&si->lock);
     put_swap_device(si);
 outer:
     if (page)
         __free_page(page);
     return ret;
 }
 
 /*
  * swap_count_continued - when the original swap_map count is incremented
  * from SWAP_MAP_MAX, check if there is already a continuation page to carry
  * into, carry if so, or else fail until a new continuation page is allocated;
  * when the original swap_map count is decremented from 0 with continuation,
  * borrow from the continuation and report whether it still holds more.
  * Called while __swap_duplicate() or swap_entry_free() holds swap or cluster
  * lock.
  */
 static bool swap_count_continued(struct swap_info_struct *si,
                  pgoff_t offset, unsigned char count)
 {
     struct page *head;
     struct page *page;
     unsigned char *map;
     bool ret;
 
     head = vmalloc_to_page(si->swap_map + offset);
     if (page_private(head) != SWP_CONTINUED) {
         BUG_ON(count & COUNT_CONTINUED);
         return false;       /* need to add count continuation */
     }
 
     spin_lock(&si->cont_lock);
     offset &= ~PAGE_MASK;
     page = list_next_entry(head, lru);
     map = kmap_atomic(page) + offset;
 
     if (count == SWAP_MAP_MAX)  /* initial increment from swap_map */
         goto init_map;      /* jump over SWAP_CONT_MAX checks */
 
     if (count == (SWAP_MAP_MAX | COUNT_CONTINUED)) { /* incrementing */
         /*
          * Think of how you add 1 to 999
          */
         while (*map == (SWAP_CONT_MAX | COUNT_CONTINUED)) {
             kunmap_atomic(map);
             page = list_next_entry(page, lru);
             BUG_ON(page == head);
             map = kmap_atomic(page) + offset;
         }
         if (*map == SWAP_CONT_MAX) {
             kunmap_atomic(map);
             page = list_next_entry(page, lru);
             if (page == head) {
                 ret = false;    /* add count continuation */
                 goto out;
             }
             map = kmap_atomic(page) + offset;
 init_map:       *map = 0;       /* we didn't zero the page */
         }
         *map += 1;
         kunmap_atomic(map);
         while ((page = list_prev_entry(page, lru)) != head) {
             map = kmap_atomic(page) + offset;
             *map = COUNT_CONTINUED;
             kunmap_atomic(map);
         }
         ret = true;         /* incremented */
 
     } else {                /* decrementing */
         /*
          * Think of how you subtract 1 from 1000
          */
         BUG_ON(count != COUNT_CONTINUED);
         while (*map == COUNT_CONTINUED) {
             kunmap_atomic(map);
             page = list_next_entry(page, lru);
             BUG_ON(page == head);
             map = kmap_atomic(page) + offset;
         }
         BUG_ON(*map == 0);
         *map -= 1;
         if (*map == 0)
             count = 0;
         kunmap_atomic(map);
         while ((page = list_prev_entry(page, lru)) != head) {
             map = kmap_atomic(page) + offset;
             *map = SWAP_CONT_MAX | count;
             count = COUNT_CONTINUED;
             kunmap_atomic(map);
         }
         ret = count == COUNT_CONTINUED;
     }
 out:
     spin_unlock(&si->cont_lock);
     return ret;
 }
 
 /*
  * free_swap_count_continuations - swapoff free all the continuation pages
  * appended to the swap_map, after swap_map is quiesced, before vfree'ing it.
  */
 static void free_swap_count_continuations(struct swap_info_struct *si)
 {
     pgoff_t offset;
 
     for (offset = 0; offset < si->max; offset += PAGE_SIZE) {
         struct page *head;
         head = vmalloc_to_page(si->swap_map + offset);
         if (page_private(head)) {
             struct page *page, *next;
 
             list_for_each_entry_safe(page, next, &head->lru, lru) {
                 list_del(&page->lru);
                 __free_page(page);
             }
         }
     }
 }
 
 #if defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
 void __cgroup_throttle_swaprate(struct page *page, gfp_t gfp_mask)
 {
     struct swap_info_struct *si, *next;
     int nid = page_to_nid(page);
 
     if (!(gfp_mask & __GFP_IO))
         return;
 
     if (!blk_cgroup_congested())
         return;
 
     /*
      * We've already scheduled a throttle, avoid taking the global swap
      * lock.
      */
     if (current->throttle_queue)
         return;
 
     spin_lock(&swap_avail_lock);
     plist_for_each_entry_safe(si, next, &swap_avail_heads[nid],
                   avail_lists[nid]) {
         if (si->bdev) {
             blkcg_schedule_throttle(bdev_get_queue(si->bdev), true);
             break;
         }
     }
     spin_unlock(&swap_avail_lock);
 }
 #endif
 
 static int __init swapfile_init(void)
 {
     int nid;
 
     swap_avail_heads = kmalloc_array(nr_node_ids, sizeof(struct plist_head),
                      GFP_KERNEL);
     if (!swap_avail_heads) {
         pr_emerg("Not enough memory for swap heads, swap is disabled\n");
         return -ENOMEM;
     }
 
     for_each_node(nid)
         plist_head_init(&swap_avail_heads[nid]);
 
     return 0;
 }
 subsys_initcall(swapfile_init);