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 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * z3fold.c
  *
  * Author: Vitaly Wool <vitaly.wool@konsulko.com>
  * Copyright (C) 2016, Sony Mobile Communications Inc.
  *
  * This implementation is based on zbud written by Seth Jennings.
  *
  * z3fold is an special purpose allocator for storing compressed pages. It
  * can store up to three compressed pages per page which improves the
  * compression ratio of zbud while retaining its main concepts (e. g. always
  * storing an integral number of objects per page) and simplicity.
  * It still has simple and deterministic reclaim properties that make it
  * preferable to a higher density approach (with no requirement on integral
  * number of object per page) when reclaim is used.
  *
  * As in zbud, pages are divided into "chunks".  The size of the chunks is
  * fixed at compile time and is determined by NCHUNKS_ORDER below.
  *
  * z3fold doesn't export any API and is meant to be used via zpool API.
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/atomic.h>
 #include <linux/sched.h>
 #include <linux/cpumask.h>
 #include <linux/list.h>
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/page-flags.h>
 #include <linux/migrate.h>
 #include <linux/node.h>
 #include <linux/compaction.h>
 #include <linux/percpu.h>
 #include <linux/preempt.h>
 #include <linux/workqueue.h>
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/zpool.h>
 #include <linux/kmemleak.h>
 
 /*
  * NCHUNKS_ORDER determines the internal allocation granularity, effectively
  * adjusting internal fragmentation.  It also determines the number of
  * freelists maintained in each pool. NCHUNKS_ORDER of 6 means that the
  * allocation granularity will be in chunks of size PAGE_SIZE/64. Some chunks
  * in the beginning of an allocated page are occupied by z3fold header, so
  * NCHUNKS will be calculated to 63 (or 62 in case CONFIG_DEBUG_SPINLOCK=y),
  * which shows the max number of free chunks in z3fold page, also there will
  * be 63, or 62, respectively, freelists per pool.
  */
 #define NCHUNKS_ORDER   6
 
 #define CHUNK_SHIFT (PAGE_SHIFT - NCHUNKS_ORDER)
 #define CHUNK_SIZE  (1 << CHUNK_SHIFT)
 #define ZHDR_SIZE_ALIGNED round_up(sizeof(struct z3fold_header), CHUNK_SIZE)
 #define ZHDR_CHUNKS (ZHDR_SIZE_ALIGNED >> CHUNK_SHIFT)
 #define TOTAL_CHUNKS    (PAGE_SIZE >> CHUNK_SHIFT)
 #define NCHUNKS     (TOTAL_CHUNKS - ZHDR_CHUNKS)
 
 #define BUDDY_MASK  (0x3)
 #define BUDDY_SHIFT 2
 #define SLOTS_ALIGN (0x40)
 
 /*****************
  * Structures
 *****************/
 struct z3fold_pool;
 struct z3fold_ops {
     int (*evict)(struct z3fold_pool *pool, unsigned long handle);
 };
 
 enum buddy {
     HEADLESS = 0,
     FIRST,
     MIDDLE,
     LAST,
     BUDDIES_MAX = LAST
 };
 
 struct z3fold_buddy_slots {
     /*
      * we are using BUDDY_MASK in handle_to_buddy etc. so there should
      * be enough slots to hold all possible variants
      */
     unsigned long slot[BUDDY_MASK + 1];
     unsigned long pool; /* back link */
     rwlock_t lock;
 };
 #define HANDLE_FLAG_MASK    (0x03)
 
 /*
  * struct z3fold_header - z3fold page metadata occupying first chunks of each
  *          z3fold page, except for HEADLESS pages
  * @buddy:      links the z3fold page into the relevant list in the
  *          pool
  * @page_lock:      per-page lock
  * @refcount:       reference count for the z3fold page
  * @work:       work_struct for page layout optimization
  * @slots:      pointer to the structure holding buddy slots
  * @pool:       pointer to the containing pool
  * @cpu:        CPU which this page "belongs" to
  * @first_chunks:   the size of the first buddy in chunks, 0 if free
  * @middle_chunks:  the size of the middle buddy in chunks, 0 if free
  * @last_chunks:    the size of the last buddy in chunks, 0 if free
  * @first_num:      the starting number (for the first handle)
  * @mapped_count:   the number of objects currently mapped
  */
 struct z3fold_header {
     struct list_head buddy;
     spinlock_t page_lock;
     struct kref refcount;
     struct work_struct work;
     struct z3fold_buddy_slots *slots;
     struct z3fold_pool *pool;
     short cpu;
     unsigned short first_chunks;
     unsigned short middle_chunks;
     unsigned short last_chunks;
     unsigned short start_middle;
     unsigned short first_num:2;
     unsigned short mapped_count:2;
     unsigned short foreign_handles:2;
 };
 
 /**
  * struct z3fold_pool - stores metadata for each z3fold pool
  * @name:   pool name
  * @lock:   protects pool unbuddied/lru lists
  * @stale_lock: protects pool stale page list
  * @unbuddied:  per-cpu array of lists tracking z3fold pages that contain 2-
  *      buddies; the list each z3fold page is added to depends on
  *      the size of its free region.
  * @lru:    list tracking the z3fold pages in LRU order by most recently
  *      added buddy.
  * @stale:  list of pages marked for freeing
  * @pages_nr:   number of z3fold pages in the pool.
  * @c_handle:   cache for z3fold_buddy_slots allocation
  * @ops:    pointer to a structure of user defined operations specified at
  *      pool creation time.
  * @zpool:  zpool driver
  * @zpool_ops:  zpool operations structure with an evict callback
  * @compact_wq: workqueue for page layout background optimization
  * @release_wq: workqueue for safe page release
  * @work:   work_struct for safe page release
  *
  * This structure is allocated at pool creation time and maintains metadata
  * pertaining to a particular z3fold pool.
  */
 struct z3fold_pool {
     const char *name;
     spinlock_t lock;
     spinlock_t stale_lock;
     struct list_head *unbuddied;
     struct list_head lru;
     struct list_head stale;
     atomic64_t pages_nr;
     struct kmem_cache *c_handle;
     const struct z3fold_ops *ops;
     struct zpool *zpool;
     const struct zpool_ops *zpool_ops;
     struct workqueue_struct *compact_wq;
     struct workqueue_struct *release_wq;
     struct work_struct work;
 };
 
 /*
  * Internal z3fold page flags
  */
 enum z3fold_page_flags {
     PAGE_HEADLESS = 0,
     MIDDLE_CHUNK_MAPPED,
     NEEDS_COMPACTING,
     PAGE_STALE,
     PAGE_CLAIMED, /* by either reclaim or free */
     PAGE_MIGRATED, /* page is migrated and soon to be released */
 };
 
 /*
  * handle flags, go under HANDLE_FLAG_MASK
  */
 enum z3fold_handle_flags {
     HANDLES_NOFREE = 0,
 };
 
 /*
  * Forward declarations
  */
 static struct z3fold_header *__z3fold_alloc(struct z3fold_pool *, size_t, bool);
 static void compact_page_work(struct work_struct *w);
 
 /*****************
  * Helpers
 *****************/
 
 /* Converts an allocation size in bytes to size in z3fold chunks */
 static int size_to_chunks(size_t size)
 {
     return (size + CHUNK_SIZE - 1) >> CHUNK_SHIFT;
 }
 
 #define for_each_unbuddied_list(_iter, _begin) \
     for ((_iter) = (_begin); (_iter) < NCHUNKS; (_iter)++)
 
 static inline struct z3fold_buddy_slots *alloc_slots(struct z3fold_pool *pool,
                             gfp_t gfp)
 {
     struct z3fold_buddy_slots *slots = kmem_cache_zalloc(pool->c_handle,
                                  gfp);
 
     if (slots) {
         /* It will be freed separately in free_handle(). */
         kmemleak_not_leak(slots);
         slots->pool = (unsigned long)pool;
         rwlock_init(&slots->lock);
     }
 
     return slots;
 }
 
 static inline struct z3fold_pool *slots_to_pool(struct z3fold_buddy_slots *s)
 {
     return (struct z3fold_pool *)(s->pool & ~HANDLE_FLAG_MASK);
 }
 
 static inline struct z3fold_buddy_slots *handle_to_slots(unsigned long handle)
 {
     return (struct z3fold_buddy_slots *)(handle & ~(SLOTS_ALIGN - 1));
 }
 
 /* Lock a z3fold page */
 static inline void z3fold_page_lock(struct z3fold_header *zhdr)
 {
     spin_lock(&zhdr->page_lock);
 }
 
 /* Try to lock a z3fold page */
 static inline int z3fold_page_trylock(struct z3fold_header *zhdr)
 {
     return spin_trylock(&zhdr->page_lock);
 }
 
 /* Unlock a z3fold page */
 static inline void z3fold_page_unlock(struct z3fold_header *zhdr)
 {
     spin_unlock(&zhdr->page_lock);
 }
 
 /* return locked z3fold page if it's not headless */
 static inline struct z3fold_header *get_z3fold_header(unsigned long handle)
 {
     struct z3fold_buddy_slots *slots;
     struct z3fold_header *zhdr;
     int locked = 0;
 
     if (!(handle & (1 << PAGE_HEADLESS))) {
         slots = handle_to_slots(handle);
         do {
             unsigned long addr;
 
             read_lock(&slots->lock);
             addr = *(unsigned long *)handle;
             zhdr = (struct z3fold_header *)(addr & PAGE_MASK);
             locked = z3fold_page_trylock(zhdr);
             read_unlock(&slots->lock);
             if (locked) {
                 struct page *page = virt_to_page(zhdr);
 
                 if (!test_bit(PAGE_MIGRATED, &page->private))
                     break;
                 z3fold_page_unlock(zhdr);
             }
             cpu_relax();
         } while (true);
     } else {
         zhdr = (struct z3fold_header *)(handle & PAGE_MASK);
     }
 
     return zhdr;
 }
 
 static inline void put_z3fold_header(struct z3fold_header *zhdr)
 {
     struct page *page = virt_to_page(zhdr);
 
     if (!test_bit(PAGE_HEADLESS, &page->private))
         z3fold_page_unlock(zhdr);
 }
 
 static inline void free_handle(unsigned long handle, struct z3fold_header *zhdr)
 {
     struct z3fold_buddy_slots *slots;
     int i;
     bool is_free;
 
     if (WARN_ON(*(unsigned long *)handle == 0))
         return;
 
     slots = handle_to_slots(handle);
     write_lock(&slots->lock);
     *(unsigned long *)handle = 0;
 
     if (test_bit(HANDLES_NOFREE, &slots->pool)) {
         write_unlock(&slots->lock);
         return; /* simple case, nothing else to do */
     }
 
     if (zhdr->slots != slots)
         zhdr->foreign_handles--;
 
     is_free = true;
     for (i = 0; i <= BUDDY_MASK; i++) {
         if (slots->slot[i]) {
             is_free = false;
             break;
         }
     }
     write_unlock(&slots->lock);
 
     if (is_free) {
         struct z3fold_pool *pool = slots_to_pool(slots);
 
         if (zhdr->slots == slots)
             zhdr->slots = NULL;
         kmem_cache_free(pool->c_handle, slots);
     }
 }
 
 /* Initializes the z3fold header of a newly allocated z3fold page */
 static struct z3fold_header *init_z3fold_page(struct page *page, bool headless,
                     struct z3fold_pool *pool, gfp_t gfp)
 {
     struct z3fold_header *zhdr = page_address(page);
     struct z3fold_buddy_slots *slots;
 
     INIT_LIST_HEAD(&page->lru);
     clear_bit(PAGE_HEADLESS, &page->private);
     clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
     clear_bit(NEEDS_COMPACTING, &page->private);
     clear_bit(PAGE_STALE, &page->private);
     clear_bit(PAGE_CLAIMED, &page->private);
     clear_bit(PAGE_MIGRATED, &page->private);
     if (headless)
         return zhdr;
 
     slots = alloc_slots(pool, gfp);
     if (!slots)
         return NULL;
 
     memset(zhdr, 0, sizeof(*zhdr));
     spin_lock_init(&zhdr->page_lock);
     kref_init(&zhdr->refcount);
     zhdr->cpu = -1;
     zhdr->slots = slots;
     zhdr->pool = pool;
     INIT_LIST_HEAD(&zhdr->buddy);
     INIT_WORK(&zhdr->work, compact_page_work);
     return zhdr;
 }
 
 /* Resets the struct page fields and frees the page */
 static void free_z3fold_page(struct page *page, bool headless)
 {
     if (!headless) {
         lock_page(page);
         __ClearPageMovable(page);
         unlock_page(page);
     }
     __free_page(page);
 }
 
 /* Helper function to build the index */
 static inline int __idx(struct z3fold_header *zhdr, enum buddy bud)
 {
     return (bud + zhdr->first_num) & BUDDY_MASK;
 }
 
 /*
  * Encodes the handle of a particular buddy within a z3fold page
  * Pool lock should be held as this function accesses first_num
  */
 static unsigned long __encode_handle(struct z3fold_header *zhdr,
                 struct z3fold_buddy_slots *slots,
                 enum buddy bud)
 {
     unsigned long h = (unsigned long)zhdr;
     int idx = 0;
 
     /*
      * For a headless page, its handle is its pointer with the extra
      * PAGE_HEADLESS bit set
      */
     if (bud == HEADLESS)
         return h | (1 << PAGE_HEADLESS);
 
     /* otherwise, return pointer to encoded handle */
     idx = __idx(zhdr, bud);
     h += idx;
     if (bud == LAST)
         h |= (zhdr->last_chunks << BUDDY_SHIFT);
 
     write_lock(&slots->lock);
     slots->slot[idx] = h;
     write_unlock(&slots->lock);
     return (unsigned long)&slots->slot[idx];
 }
 
 static unsigned long encode_handle(struct z3fold_header *zhdr, enum buddy bud)
 {
     return __encode_handle(zhdr, zhdr->slots, bud);
 }
 
 /* only for LAST bud, returns zero otherwise */
 static unsigned short handle_to_chunks(unsigned long handle)
 {
     struct z3fold_buddy_slots *slots = handle_to_slots(handle);
     unsigned long addr;
 
     read_lock(&slots->lock);
     addr = *(unsigned long *)handle;
     read_unlock(&slots->lock);
     return (addr & ~PAGE_MASK) >> BUDDY_SHIFT;
 }
 
 /*
  * (handle & BUDDY_MASK) < zhdr->first_num is possible in encode_handle
  *  but that doesn't matter. because the masking will result in the
  *  correct buddy number.
  */
 static enum buddy handle_to_buddy(unsigned long handle)
 {
     struct z3fold_header *zhdr;
     struct z3fold_buddy_slots *slots = handle_to_slots(handle);
     unsigned long addr;
 
     read_lock(&slots->lock);
     WARN_ON(handle & (1 << PAGE_HEADLESS));
     addr = *(unsigned long *)handle;
     read_unlock(&slots->lock);
     zhdr = (struct z3fold_header *)(addr & PAGE_MASK);
     return (addr - zhdr->first_num) & BUDDY_MASK;
 }
 
 static inline struct z3fold_pool *zhdr_to_pool(struct z3fold_header *zhdr)
 {
     return zhdr->pool;
 }
 
 static void __release_z3fold_page(struct z3fold_header *zhdr, bool locked)
 {
     struct page *page = virt_to_page(zhdr);
     struct z3fold_pool *pool = zhdr_to_pool(zhdr);
 
     WARN_ON(!list_empty(&zhdr->buddy));
     set_bit(PAGE_STALE, &page->private);
     clear_bit(NEEDS_COMPACTING, &page->private);
     spin_lock(&pool->lock);
     if (!list_empty(&page->lru))
         list_del_init(&page->lru);
     spin_unlock(&pool->lock);
 
     if (locked)
         z3fold_page_unlock(zhdr);
 
     spin_lock(&pool->stale_lock);
     list_add(&zhdr->buddy, &pool->stale);
     queue_work(pool->release_wq, &pool->work);
     spin_unlock(&pool->stale_lock);
 
     atomic64_dec(&pool->pages_nr);
 }
 
 static void release_z3fold_page_locked(struct kref *ref)
 {
     struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
                         refcount);
     WARN_ON(z3fold_page_trylock(zhdr));
     __release_z3fold_page(zhdr, true);
 }
 
 static void release_z3fold_page_locked_list(struct kref *ref)
 {
     struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
                            refcount);
     struct z3fold_pool *pool = zhdr_to_pool(zhdr);
 
     spin_lock(&pool->lock);
     list_del_init(&zhdr->buddy);
     spin_unlock(&pool->lock);
 
     WARN_ON(z3fold_page_trylock(zhdr));
     __release_z3fold_page(zhdr, true);
 }
 
 static void free_pages_work(struct work_struct *w)
 {
     struct z3fold_pool *pool = container_of(w, struct z3fold_pool, work);
 
     spin_lock(&pool->stale_lock);
     while (!list_empty(&pool->stale)) {
         struct z3fold_header *zhdr = list_first_entry(&pool->stale,
                         struct z3fold_header, buddy);
         struct page *page = virt_to_page(zhdr);
 
         list_del(&zhdr->buddy);
         if (WARN_ON(!test_bit(PAGE_STALE, &page->private)))
             continue;
         spin_unlock(&pool->stale_lock);
         cancel_work_sync(&zhdr->work);
         free_z3fold_page(page, false);
         cond_resched();
         spin_lock(&pool->stale_lock);
     }
     spin_unlock(&pool->stale_lock);
 }
 
 /*
  * Returns the number of free chunks in a z3fold page.
  * NB: can't be used with HEADLESS pages.
  */
 static int num_free_chunks(struct z3fold_header *zhdr)
 {
     int nfree;
     /*
      * If there is a middle object, pick up the bigger free space
      * either before or after it. Otherwise just subtract the number
      * of chunks occupied by the first and the last objects.
      */
     if (zhdr->middle_chunks != 0) {
         int nfree_before = zhdr->first_chunks ?
             0 : zhdr->start_middle - ZHDR_CHUNKS;
         int nfree_after = zhdr->last_chunks ?
             0 : TOTAL_CHUNKS -
                 (zhdr->start_middle + zhdr->middle_chunks);
         nfree = max(nfree_before, nfree_after);
     } else
         nfree = NCHUNKS - zhdr->first_chunks - zhdr->last_chunks;
     return nfree;
 }
 
 /* Add to the appropriate unbuddied list */
 static inline void add_to_unbuddied(struct z3fold_pool *pool,
                 struct z3fold_header *zhdr)
 {
     if (zhdr->first_chunks == 0 || zhdr->last_chunks == 0 ||
             zhdr->middle_chunks == 0) {
         struct list_head *unbuddied;
         int freechunks = num_free_chunks(zhdr);
 
         migrate_disable();
         unbuddied = this_cpu_ptr(pool->unbuddied);
         spin_lock(&pool->lock);
         list_add(&zhdr->buddy, &unbuddied[freechunks]);
         spin_unlock(&pool->lock);
         zhdr->cpu = smp_processor_id();
         migrate_enable();
     }
 }
 
 static inline enum buddy get_free_buddy(struct z3fold_header *zhdr, int chunks)
 {
     enum buddy bud = HEADLESS;
 
     if (zhdr->middle_chunks) {
         if (!zhdr->first_chunks &&
             chunks <= zhdr->start_middle - ZHDR_CHUNKS)
             bud = FIRST;
         else if (!zhdr->last_chunks)
             bud = LAST;
     } else {
         if (!zhdr->first_chunks)
             bud = FIRST;
         else if (!zhdr->last_chunks)
             bud = LAST;
         else
             bud = MIDDLE;
     }
 
     return bud;
 }
 
 static inline void *mchunk_memmove(struct z3fold_header *zhdr,
                 unsigned short dst_chunk)
 {
     void *beg = zhdr;
     return memmove(beg + (dst_chunk << CHUNK_SHIFT),
                beg + (zhdr->start_middle << CHUNK_SHIFT),
                zhdr->middle_chunks << CHUNK_SHIFT);
 }
 
 static inline bool buddy_single(struct z3fold_header *zhdr)
 {
     return !((zhdr->first_chunks && zhdr->middle_chunks) ||
             (zhdr->first_chunks && zhdr->last_chunks) ||
             (zhdr->middle_chunks && zhdr->last_chunks));
 }
 
 static struct z3fold_header *compact_single_buddy(struct z3fold_header *zhdr)
 {
     struct z3fold_pool *pool = zhdr_to_pool(zhdr);
     void *p = zhdr;
     unsigned long old_handle = 0;
     size_t sz = 0;
     struct z3fold_header *new_zhdr = NULL;
     int first_idx = __idx(zhdr, FIRST);
     int middle_idx = __idx(zhdr, MIDDLE);
     int last_idx = __idx(zhdr, LAST);
     unsigned short *moved_chunks = NULL;
 
     /*
      * No need to protect slots here -- all the slots are "local" and
      * the page lock is already taken
      */
     if (zhdr->first_chunks && zhdr->slots->slot[first_idx]) {
         p += ZHDR_SIZE_ALIGNED;
         sz = zhdr->first_chunks << CHUNK_SHIFT;
         old_handle = (unsigned long)&zhdr->slots->slot[first_idx];
         moved_chunks = &zhdr->first_chunks;
     } else if (zhdr->middle_chunks && zhdr->slots->slot[middle_idx]) {
         p += zhdr->start_middle << CHUNK_SHIFT;
         sz = zhdr->middle_chunks << CHUNK_SHIFT;
         old_handle = (unsigned long)&zhdr->slots->slot[middle_idx];
         moved_chunks = &zhdr->middle_chunks;
     } else if (zhdr->last_chunks && zhdr->slots->slot[last_idx]) {
         p += PAGE_SIZE - (zhdr->last_chunks << CHUNK_SHIFT);
         sz = zhdr->last_chunks << CHUNK_SHIFT;
         old_handle = (unsigned long)&zhdr->slots->slot[last_idx];
         moved_chunks = &zhdr->last_chunks;
     }
 
     if (sz > 0) {
         enum buddy new_bud = HEADLESS;
         short chunks = size_to_chunks(sz);
         void *q;
 
         new_zhdr = __z3fold_alloc(pool, sz, false);
         if (!new_zhdr)
             return NULL;
 
         if (WARN_ON(new_zhdr == zhdr))
             goto out_fail;
 
         new_bud = get_free_buddy(new_zhdr, chunks);
         q = new_zhdr;
         switch (new_bud) {
         case FIRST:
             new_zhdr->first_chunks = chunks;
             q += ZHDR_SIZE_ALIGNED;
             break;
         case MIDDLE:
             new_zhdr->middle_chunks = chunks;
             new_zhdr->start_middle =
                 new_zhdr->first_chunks + ZHDR_CHUNKS;
             q += new_zhdr->start_middle << CHUNK_SHIFT;
             break;
         case LAST:
             new_zhdr->last_chunks = chunks;
             q += PAGE_SIZE - (new_zhdr->last_chunks << CHUNK_SHIFT);
             break;
         default:
             goto out_fail;
         }
         new_zhdr->foreign_handles++;
         memcpy(q, p, sz);
         write_lock(&zhdr->slots->lock);
         *(unsigned long *)old_handle = (unsigned long)new_zhdr +
             __idx(new_zhdr, new_bud);
         if (new_bud == LAST)
             *(unsigned long *)old_handle |=
                     (new_zhdr->last_chunks << BUDDY_SHIFT);
         write_unlock(&zhdr->slots->lock);
         add_to_unbuddied(pool, new_zhdr);
         z3fold_page_unlock(new_zhdr);
 
         *moved_chunks = 0;
     }
 
     return new_zhdr;
 
 out_fail:
     if (new_zhdr && !kref_put(&new_zhdr->refcount, release_z3fold_page_locked)) {
         add_to_unbuddied(pool, new_zhdr);
         z3fold_page_unlock(new_zhdr);
     }
     return NULL;
 
 }
 
 #define BIG_CHUNK_GAP   3
 /* Has to be called with lock held */
 static int z3fold_compact_page(struct z3fold_header *zhdr)
 {
     struct page *page = virt_to_page(zhdr);
 
     if (test_bit(MIDDLE_CHUNK_MAPPED, &page->private))
         return 0; /* can't move middle chunk, it's used */
 
     if (unlikely(PageIsolated(page)))
         return 0;
 
     if (zhdr->middle_chunks == 0)
         return 0; /* nothing to compact */
 
     if (zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
         /* move to the beginning */
         mchunk_memmove(zhdr, ZHDR_CHUNKS);
         zhdr->first_chunks = zhdr->middle_chunks;
         zhdr->middle_chunks = 0;
         zhdr->start_middle = 0;
         zhdr->first_num++;
         return 1;
     }
 
     /*
      * moving data is expensive, so let's only do that if
      * there's substantial gain (at least BIG_CHUNK_GAP chunks)
      */
     if (zhdr->first_chunks != 0 && zhdr->last_chunks == 0 &&
         zhdr->start_middle - (zhdr->first_chunks + ZHDR_CHUNKS) >=
             BIG_CHUNK_GAP) {
         mchunk_memmove(zhdr, zhdr->first_chunks + ZHDR_CHUNKS);
         zhdr->start_middle = zhdr->first_chunks + ZHDR_CHUNKS;
         return 1;
     } else if (zhdr->last_chunks != 0 && zhdr->first_chunks == 0 &&
            TOTAL_CHUNKS - (zhdr->last_chunks + zhdr->start_middle
                     + zhdr->middle_chunks) >=
             BIG_CHUNK_GAP) {
         unsigned short new_start = TOTAL_CHUNKS - zhdr->last_chunks -
             zhdr->middle_chunks;
         mchunk_memmove(zhdr, new_start);
         zhdr->start_middle = new_start;
         return 1;
     }
 
     return 0;
 }
 
 static void do_compact_page(struct z3fold_header *zhdr, bool locked)
 {
     struct z3fold_pool *pool = zhdr_to_pool(zhdr);
     struct page *page;
 
     page = virt_to_page(zhdr);
     if (locked)
         WARN_ON(z3fold_page_trylock(zhdr));
     else
         z3fold_page_lock(zhdr);
     if (WARN_ON(!test_and_clear_bit(NEEDS_COMPACTING, &page->private))) {
         z3fold_page_unlock(zhdr);
         return;
     }
     spin_lock(&pool->lock);
     list_del_init(&zhdr->buddy);
     spin_unlock(&pool->lock);
 
     if (kref_put(&zhdr->refcount, release_z3fold_page_locked))
         return;
 
     if (test_bit(PAGE_STALE, &page->private) ||
         test_and_set_bit(PAGE_CLAIMED, &page->private)) {
         z3fold_page_unlock(zhdr);
         return;
     }
 
     if (!zhdr->foreign_handles && buddy_single(zhdr) &&
         zhdr->mapped_count == 0 && compact_single_buddy(zhdr)) {
         if (!kref_put(&zhdr->refcount, release_z3fold_page_locked)) {
             clear_bit(PAGE_CLAIMED, &page->private);
             z3fold_page_unlock(zhdr);
         }
         return;
     }
 
     z3fold_compact_page(zhdr);
     add_to_unbuddied(pool, zhdr);
     clear_bit(PAGE_CLAIMED, &page->private);
     z3fold_page_unlock(zhdr);
 }
 
 static void compact_page_work(struct work_struct *w)
 {
     struct z3fold_header *zhdr = container_of(w, struct z3fold_header,
                         work);
 
     do_compact_page(zhdr, false);
 }
 
 /* returns _locked_ z3fold page header or NULL */
 static inline struct z3fold_header *__z3fold_alloc(struct z3fold_pool *pool,
                         size_t size, bool can_sleep)
 {
     struct z3fold_header *zhdr = NULL;
     struct page *page;
     struct list_head *unbuddied;
     int chunks = size_to_chunks(size), i;
 
 lookup:
     migrate_disable();
     /* First, try to find an unbuddied z3fold page. */
     unbuddied = this_cpu_ptr(pool->unbuddied);
     for_each_unbuddied_list(i, chunks) {
         struct list_head *l = &unbuddied[i];
 
         zhdr = list_first_entry_or_null(READ_ONCE(l),
                     struct z3fold_header, buddy);
 
         if (!zhdr)
             continue;
 
         /* Re-check under lock. */
         spin_lock(&pool->lock);
         if (unlikely(zhdr != list_first_entry(READ_ONCE(l),
                         struct z3fold_header, buddy)) ||
             !z3fold_page_trylock(zhdr)) {
             spin_unlock(&pool->lock);
             zhdr = NULL;
             migrate_enable();
             if (can_sleep)
                 cond_resched();
             goto lookup;
         }
         list_del_init(&zhdr->buddy);
         zhdr->cpu = -1;
         spin_unlock(&pool->lock);
 
         page = virt_to_page(zhdr);
         if (test_bit(NEEDS_COMPACTING, &page->private) ||
             test_bit(PAGE_CLAIMED, &page->private)) {
             z3fold_page_unlock(zhdr);
             zhdr = NULL;
             migrate_enable();
             if (can_sleep)
                 cond_resched();
             goto lookup;
         }
 
         /*
          * this page could not be removed from its unbuddied
          * list while pool lock was held, and then we've taken
          * page lock so kref_put could not be called before
          * we got here, so it's safe to just call kref_get()
          */
         kref_get(&zhdr->refcount);
         break;
     }
     migrate_enable();
 
     if (!zhdr) {
         int cpu;
 
         /* look for _exact_ match on other cpus' lists */
         for_each_online_cpu(cpu) {
             struct list_head *l;
 
             unbuddied = per_cpu_ptr(pool->unbuddied, cpu);
             spin_lock(&pool->lock);
             l = &unbuddied[chunks];
 
             zhdr = list_first_entry_or_null(READ_ONCE(l),
                         struct z3fold_header, buddy);
 
             if (!zhdr || !z3fold_page_trylock(zhdr)) {
                 spin_unlock(&pool->lock);
                 zhdr = NULL;
                 continue;
             }
             list_del_init(&zhdr->buddy);
             zhdr->cpu = -1;
             spin_unlock(&pool->lock);
 
             page = virt_to_page(zhdr);
             if (test_bit(NEEDS_COMPACTING, &page->private) ||
                 test_bit(PAGE_CLAIMED, &page->private)) {
                 z3fold_page_unlock(zhdr);
                 zhdr = NULL;
                 if (can_sleep)
                     cond_resched();
                 continue;
             }
             kref_get(&zhdr->refcount);
             break;
         }
     }
 
     if (zhdr && !zhdr->slots) {
         zhdr->slots = alloc_slots(pool, GFP_ATOMIC);
         if (!zhdr->slots)
             goto out_fail;
     }
     return zhdr;
 
 out_fail:
     if (!kref_put(&zhdr->refcount, release_z3fold_page_locked)) {
         add_to_unbuddied(pool, zhdr);
         z3fold_page_unlock(zhdr);
     }
     return NULL;
 }
 
 /*
  * API Functions
  */
 
 /**
  * z3fold_create_pool() - create a new z3fold pool
  * @name:   pool name
  * @gfp:    gfp flags when allocating the z3fold pool structure
  * @ops:    user-defined operations for the z3fold pool
  *
  * Return: pointer to the new z3fold pool or NULL if the metadata allocation
  * failed.
  */
 static struct z3fold_pool *z3fold_create_pool(const char *name, gfp_t gfp,
         const struct z3fold_ops *ops)
 {
     struct z3fold_pool *pool = NULL;
     int i, cpu;
 
     pool = kzalloc(sizeof(struct z3fold_pool), gfp);
     if (!pool)
         goto out;
     pool->c_handle = kmem_cache_create("z3fold_handle",
                 sizeof(struct z3fold_buddy_slots),
                 SLOTS_ALIGN, 0, NULL);
     if (!pool->c_handle)
         goto out_c;
     spin_lock_init(&pool->lock);
     spin_lock_init(&pool->stale_lock);
     pool->unbuddied = __alloc_percpu(sizeof(struct list_head) * NCHUNKS,
                      __alignof__(struct list_head));
     if (!pool->unbuddied)
         goto out_pool;
     for_each_possible_cpu(cpu) {
         struct list_head *unbuddied =
                 per_cpu_ptr(pool->unbuddied, cpu);
         for_each_unbuddied_list(i, 0)
             INIT_LIST_HEAD(&unbuddied[i]);
     }
     INIT_LIST_HEAD(&pool->lru);
     INIT_LIST_HEAD(&pool->stale);
     atomic64_set(&pool->pages_nr, 0);
     pool->name = name;
     pool->compact_wq = create_singlethread_workqueue(pool->name);
     if (!pool->compact_wq)
         goto out_unbuddied;
     pool->release_wq = create_singlethread_workqueue(pool->name);
     if (!pool->release_wq)
         goto out_wq;
     INIT_WORK(&pool->work, free_pages_work);
     pool->ops = ops;
     return pool;
 
 out_wq:
     destroy_workqueue(pool->compact_wq);
 out_unbuddied:
     free_percpu(pool->unbuddied);
 out_pool:
     kmem_cache_destroy(pool->c_handle);
 out_c:
     kfree(pool);
 out:
     return NULL;
 }
 
 /**
  * z3fold_destroy_pool() - destroys an existing z3fold pool
  * @pool:   the z3fold pool to be destroyed
  *
  * The pool should be emptied before this function is called.
  */
 static void z3fold_destroy_pool(struct z3fold_pool *pool)
 {
     kmem_cache_destroy(pool->c_handle);
 
     /*
      * We need to destroy pool->compact_wq before pool->release_wq,
      * as any pending work on pool->compact_wq will call
      * queue_work(pool->release_wq, &pool->work).
      *
      * There are still outstanding pages until both workqueues are drained,
      * so we cannot unregister migration until then.
      */
 
     destroy_workqueue(pool->compact_wq);
     destroy_workqueue(pool->release_wq);
     free_percpu(pool->unbuddied);
     kfree(pool);
 }
 
 static const struct movable_operations z3fold_mops;
 
 /**
  * z3fold_alloc() - allocates a region of a given size
  * @pool:   z3fold pool from which to allocate
  * @size:   size in bytes of the desired allocation
  * @gfp:    gfp flags used if the pool needs to grow
  * @handle: handle of the new allocation
  *
  * This function will attempt to find a free region in the pool large enough to
  * satisfy the allocation request.  A search of the unbuddied lists is
  * performed first. If no suitable free region is found, then a new page is
  * allocated and added to the pool to satisfy the request.
  *
  * Return: 0 if success and handle is set, otherwise -EINVAL if the size or
  * gfp arguments are invalid or -ENOMEM if the pool was unable to allocate
  * a new page.
  */
 static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
             unsigned long *handle)
 {
     int chunks = size_to_chunks(size);
     struct z3fold_header *zhdr = NULL;
     struct page *page = NULL;
     enum buddy bud;
     bool can_sleep = gfpflags_allow_blocking(gfp);
 
     if (!size || (gfp & __GFP_HIGHMEM))
         return -EINVAL;
 
     if (size > PAGE_SIZE)
         return -ENOSPC;
 
     if (size > PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE)
         bud = HEADLESS;
     else {
 retry:
         zhdr = __z3fold_alloc(pool, size, can_sleep);
         if (zhdr) {
             bud = get_free_buddy(zhdr, chunks);
             if (bud == HEADLESS) {
                 if (!kref_put(&zhdr->refcount,
                          release_z3fold_page_locked))
                     z3fold_page_unlock(zhdr);
                 pr_err("No free chunks in unbuddied\n");
                 WARN_ON(1);
                 goto retry;
             }
             page = virt_to_page(zhdr);
             goto found;
         }
         bud = FIRST;
     }
 
     page = alloc_page(gfp);
     if (!page)
         return -ENOMEM;
 
     zhdr = init_z3fold_page(page, bud == HEADLESS, pool, gfp);
     if (!zhdr) {
         __free_page(page);
         return -ENOMEM;
     }
     atomic64_inc(&pool->pages_nr);
 
     if (bud == HEADLESS) {
         set_bit(PAGE_HEADLESS, &page->private);
         goto headless;
     }
     if (can_sleep) {
         lock_page(page);
         __SetPageMovable(page, &z3fold_mops);
         unlock_page(page);
     } else {
         WARN_ON(!trylock_page(page));
         __SetPageMovable(page, &z3fold_mops);
         unlock_page(page);
     }
     z3fold_page_lock(zhdr);
 
 found:
     if (bud == FIRST)
         zhdr->first_chunks = chunks;
     else if (bud == LAST)
         zhdr->last_chunks = chunks;
     else {
         zhdr->middle_chunks = chunks;
         zhdr->start_middle = zhdr->first_chunks + ZHDR_CHUNKS;
     }
     add_to_unbuddied(pool, zhdr);
 
 headless:
     spin_lock(&pool->lock);
     /* Add/move z3fold page to beginning of LRU */
     if (!list_empty(&page->lru))
         list_del(&page->lru);
 
     list_add(&page->lru, &pool->lru);
 
     *handle = encode_handle(zhdr, bud);
     spin_unlock(&pool->lock);
     if (bud != HEADLESS)
         z3fold_page_unlock(zhdr);
 
     return 0;
 }
 
 /**
  * z3fold_free() - frees the allocation associated with the given handle
  * @pool:   pool in which the allocation resided
  * @handle: handle associated with the allocation returned by z3fold_alloc()
  *
  * In the case that the z3fold page in which the allocation resides is under
  * reclaim, as indicated by the PAGE_CLAIMED flag being set, this function
  * only sets the first|middle|last_chunks to 0.  The page is actually freed
  * once all buddies are evicted (see z3fold_reclaim_page() below).
  */
 static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
 {
     struct z3fold_header *zhdr;
     struct page *page;
     enum buddy bud;
     bool page_claimed;
 
     zhdr = get_z3fold_header(handle);
     page = virt_to_page(zhdr);
     page_claimed = test_and_set_bit(PAGE_CLAIMED, &page->private);
 
     if (test_bit(PAGE_HEADLESS, &page->private)) {
         /* if a headless page is under reclaim, just leave.
          * NB: we use test_and_set_bit for a reason: if the bit
          * has not been set before, we release this page
          * immediately so we don't care about its value any more.
          */
         if (!page_claimed) {
             spin_lock(&pool->lock);
             list_del(&page->lru);
             spin_unlock(&pool->lock);
             put_z3fold_header(zhdr);
             free_z3fold_page(page, true);
             atomic64_dec(&pool->pages_nr);
         }
         return;
     }
 
     /* Non-headless case */
     bud = handle_to_buddy(handle);
 
     switch (bud) {
     case FIRST:
         zhdr->first_chunks = 0;
         break;
     case MIDDLE:
         zhdr->middle_chunks = 0;
         break;
     case LAST:
         zhdr->last_chunks = 0;
         break;
     default:
         pr_err("%s: unknown bud %d\n", __func__, bud);
         WARN_ON(1);
         put_z3fold_header(zhdr);
         return;
     }
 
     if (!page_claimed)
         free_handle(handle, zhdr);
     if (kref_put(&zhdr->refcount, release_z3fold_page_locked_list))
         return;
     if (page_claimed) {
         /* the page has not been claimed by us */
         put_z3fold_header(zhdr);
         return;
     }
     if (test_and_set_bit(NEEDS_COMPACTING, &page->private)) {
         clear_bit(PAGE_CLAIMED, &page->private);
         put_z3fold_header(zhdr);
         return;
     }
     if (zhdr->cpu < 0 || !cpu_online(zhdr->cpu)) {
         zhdr->cpu = -1;
         kref_get(&zhdr->refcount);
         clear_bit(PAGE_CLAIMED, &page->private);
         do_compact_page(zhdr, true);
         return;
     }
     kref_get(&zhdr->refcount);
     clear_bit(PAGE_CLAIMED, &page->private);
     queue_work_on(zhdr->cpu, pool->compact_wq, &zhdr->work);
     put_z3fold_header(zhdr);
 }
 
 /**
  * z3fold_reclaim_page() - evicts allocations from a pool page and frees it
  * @pool:   pool from which a page will attempt to be evicted
  * @retries:    number of pages on the LRU list for which eviction will
  *      be attempted before failing
  *
  * z3fold reclaim is different from normal system reclaim in that it is done
  * from the bottom, up. This is because only the bottom layer, z3fold, has
  * information on how the allocations are organized within each z3fold page.
  * This has the potential to create interesting locking situations between
  * z3fold and the user, however.
  *
  * To avoid these, this is how z3fold_reclaim_page() should be called:
  *
  * The user detects a page should be reclaimed and calls z3fold_reclaim_page().
  * z3fold_reclaim_page() will remove a z3fold page from the pool LRU list and
  * call the user-defined eviction handler with the pool and handle as
  * arguments.
  *
  * If the handle can not be evicted, the eviction handler should return
  * non-zero. z3fold_reclaim_page() will add the z3fold page back to the
  * appropriate list and try the next z3fold page on the LRU up to
  * a user defined number of retries.
  *
  * If the handle is successfully evicted, the eviction handler should
  * return 0 _and_ should have called z3fold_free() on the handle. z3fold_free()
  * contains logic to delay freeing the page if the page is under reclaim,
  * as indicated by the setting of the PG_reclaim flag on the underlying page.
  *
  * If all buddies in the z3fold page are successfully evicted, then the
  * z3fold page can be freed.
  *
  * Returns: 0 if page is successfully freed, otherwise -EINVAL if there are
  * no pages to evict or an eviction handler is not registered, -EAGAIN if
  * the retry limit was hit.
  */
 static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
 {
     int i, ret = -1;
     struct z3fold_header *zhdr = NULL;
     struct page *page = NULL;
     struct list_head *pos;
     unsigned long first_handle = 0, middle_handle = 0, last_handle = 0;
     struct z3fold_buddy_slots slots __attribute__((aligned(SLOTS_ALIGN)));
 
     rwlock_init(&slots.lock);
     slots.pool = (unsigned long)pool | (1 << HANDLES_NOFREE);
 
     spin_lock(&pool->lock);
     if (!pool->ops || !pool->ops->evict || retries == 0) {
         spin_unlock(&pool->lock);
         return -EINVAL;
     }
     for (i = 0; i < retries; i++) {
         if (list_empty(&pool->lru)) {
             spin_unlock(&pool->lock);
             return -EINVAL;
         }
         list_for_each_prev(pos, &pool->lru) {
             page = list_entry(pos, struct page, lru);
 
             zhdr = page_address(page);
             if (test_bit(PAGE_HEADLESS, &page->private)) {
                 /*
                  * For non-headless pages, we wait to do this
                  * until we have the page lock to avoid racing
                  * with __z3fold_alloc(). Headless pages don't
                  * have a lock (and __z3fold_alloc() will never
                  * see them), but we still need to test and set
                  * PAGE_CLAIMED to avoid racing with
                  * z3fold_free(), so just do it now before
                  * leaving the loop.
                  */
                 if (test_and_set_bit(PAGE_CLAIMED, &page->private))
                     continue;
 
                 break;
             }
 
             if (!z3fold_page_trylock(zhdr)) {
                 zhdr = NULL;
                 continue; /* can't evict at this point */
             }
 
             /* test_and_set_bit is of course atomic, but we still
              * need to do it under page lock, otherwise checking
              * that bit in __z3fold_alloc wouldn't make sense
              */
             if (zhdr->foreign_handles ||
                 test_and_set_bit(PAGE_CLAIMED, &page->private)) {
                 z3fold_page_unlock(zhdr);
                 zhdr = NULL;
                 continue; /* can't evict such page */
             }
             list_del_init(&zhdr->buddy);
             zhdr->cpu = -1;
             /* See comment in __z3fold_alloc. */
             kref_get(&zhdr->refcount);
             break;
         }
 
         if (!zhdr)
             break;
 
         list_del_init(&page->lru);
         spin_unlock(&pool->lock);
 
         if (!test_bit(PAGE_HEADLESS, &page->private)) {
             /*
              * We need encode the handles before unlocking, and
              * use our local slots structure because z3fold_free
              * can zero out zhdr->slots and we can't do much
              * about that
              */
             first_handle = 0;
             last_handle = 0;
             middle_handle = 0;
             memset(slots.slot, 0, sizeof(slots.slot));
             if (zhdr->first_chunks)
                 first_handle = __encode_handle(zhdr, &slots,
                                 FIRST);
             if (zhdr->middle_chunks)
                 middle_handle = __encode_handle(zhdr, &slots,
                                 MIDDLE);
             if (zhdr->last_chunks)
                 last_handle = __encode_handle(zhdr, &slots,
                                 LAST);
             /*
              * it's safe to unlock here because we hold a
              * reference to this page
              */
             z3fold_page_unlock(zhdr);
         } else {
             first_handle = encode_handle(zhdr, HEADLESS);
             last_handle = middle_handle = 0;
         }
         /* Issue the eviction callback(s) */
         if (middle_handle) {
             ret = pool->ops->evict(pool, middle_handle);
             if (ret)
                 goto next;
         }
         if (first_handle) {
             ret = pool->ops->evict(pool, first_handle);
             if (ret)
                 goto next;
         }
         if (last_handle) {
             ret = pool->ops->evict(pool, last_handle);
             if (ret)
                 goto next;
         }
 next:
         if (test_bit(PAGE_HEADLESS, &page->private)) {
             if (ret == 0) {
                 free_z3fold_page(page, true);
                 atomic64_dec(&pool->pages_nr);
                 return 0;
             }
             spin_lock(&pool->lock);
             list_add(&page->lru, &pool->lru);
             spin_unlock(&pool->lock);
             clear_bit(PAGE_CLAIMED, &page->private);
         } else {
             struct z3fold_buddy_slots *slots = zhdr->slots;
             z3fold_page_lock(zhdr);
             if (kref_put(&zhdr->refcount,
                     release_z3fold_page_locked)) {
                 kmem_cache_free(pool->c_handle, slots);
                 return 0;
             }
             /*
              * if we are here, the page is still not completely
              * free. Take the global pool lock then to be able
              * to add it back to the lru list
              */
             spin_lock(&pool->lock);
             list_add(&page->lru, &pool->lru);
             spin_unlock(&pool->lock);
             if (list_empty(&zhdr->buddy))
                 add_to_unbuddied(pool, zhdr);
             clear_bit(PAGE_CLAIMED, &page->private);
             z3fold_page_unlock(zhdr);
         }
 
         /* We started off locked to we need to lock the pool back */
         spin_lock(&pool->lock);
     }
     spin_unlock(&pool->lock);
     return -EAGAIN;
 }
 
 /**
  * z3fold_map() - maps the allocation associated with the given handle
  * @pool:   pool in which the allocation resides
  * @handle: handle associated with the allocation to be mapped
  *
  * Extracts the buddy number from handle and constructs the pointer to the
  * correct starting chunk within the page.
  *
  * Returns: a pointer to the mapped allocation
  */
 static void *z3fold_map(struct z3fold_pool *pool, unsigned long handle)
 {
     struct z3fold_header *zhdr;
     struct page *page;
     void *addr;
     enum buddy buddy;
 
     zhdr = get_z3fold_header(handle);
     addr = zhdr;
     page = virt_to_page(zhdr);
 
     if (test_bit(PAGE_HEADLESS, &page->private))
         goto out;
 
     buddy = handle_to_buddy(handle);
     switch (buddy) {
     case FIRST:
         addr += ZHDR_SIZE_ALIGNED;
         break;
     case MIDDLE:
         addr += zhdr->start_middle << CHUNK_SHIFT;
         set_bit(MIDDLE_CHUNK_MAPPED, &page->private);
         break;
     case LAST:
         addr += PAGE_SIZE - (handle_to_chunks(handle) << CHUNK_SHIFT);
         break;
     default:
         pr_err("unknown buddy id %d\n", buddy);
         WARN_ON(1);
         addr = NULL;
         break;
     }
 
     if (addr)
         zhdr->mapped_count++;
 out:
     put_z3fold_header(zhdr);
     return addr;
 }
 
 /**
  * z3fold_unmap() - unmaps the allocation associated with the given handle
  * @pool:   pool in which the allocation resides
  * @handle: handle associated with the allocation to be unmapped
  */
 static void z3fold_unmap(struct z3fold_pool *pool, unsigned long handle)
 {
     struct z3fold_header *zhdr;
     struct page *page;
     enum buddy buddy;
 
     zhdr = get_z3fold_header(handle);
     page = virt_to_page(zhdr);
 
     if (test_bit(PAGE_HEADLESS, &page->private))
         return;
 
     buddy = handle_to_buddy(handle);
     if (buddy == MIDDLE)
         clear_bit(MIDDLE_CHUNK_MAPPED, &page->private);
     zhdr->mapped_count--;
     put_z3fold_header(zhdr);
 }
 
 /**
  * z3fold_get_pool_size() - gets the z3fold pool size in pages
  * @pool:   pool whose size is being queried
  *
  * Returns: size in pages of the given pool.
  */
 static u64 z3fold_get_pool_size(struct z3fold_pool *pool)
 {
     return atomic64_read(&pool->pages_nr);
 }
 
 static bool z3fold_page_isolate(struct page *page, isolate_mode_t mode)
 {
     struct z3fold_header *zhdr;
     struct z3fold_pool *pool;
 
     VM_BUG_ON_PAGE(!PageMovable(page), page);
     VM_BUG_ON_PAGE(PageIsolated(page), page);
 
     if (test_bit(PAGE_HEADLESS, &page->private))
         return false;
 
     zhdr = page_address(page);
     z3fold_page_lock(zhdr);
     if (test_bit(NEEDS_COMPACTING, &page->private) ||
         test_bit(PAGE_STALE, &page->private))
         goto out;
 
     if (zhdr->mapped_count != 0 || zhdr->foreign_handles != 0)
         goto out;
 
     if (test_and_set_bit(PAGE_CLAIMED, &page->private))
         goto out;
     pool = zhdr_to_pool(zhdr);
     spin_lock(&pool->lock);
     if (!list_empty(&zhdr->buddy))
         list_del_init(&zhdr->buddy);
     if (!list_empty(&page->lru))
         list_del_init(&page->lru);
     spin_unlock(&pool->lock);
 
     kref_get(&zhdr->refcount);
     z3fold_page_unlock(zhdr);
     return true;
 
 out:
     z3fold_page_unlock(zhdr);
     return false;
 }
 
 static int z3fold_page_migrate(struct page *newpage, struct page *page,
         enum migrate_mode mode)
 {
     struct z3fold_header *zhdr, *new_zhdr;
     struct z3fold_pool *pool;
 
     VM_BUG_ON_PAGE(!PageMovable(page), page);
     VM_BUG_ON_PAGE(!PageIsolated(page), page);
     VM_BUG_ON_PAGE(!test_bit(PAGE_CLAIMED, &page->private), page);
     VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
 
     zhdr = page_address(page);
     pool = zhdr_to_pool(zhdr);
 
     if (!z3fold_page_trylock(zhdr))
         return -EAGAIN;
     if (zhdr->mapped_count != 0 || zhdr->foreign_handles != 0) {
         clear_bit(PAGE_CLAIMED, &page->private);
         z3fold_page_unlock(zhdr);
         return -EBUSY;
     }
     if (work_pending(&zhdr->work)) {
         z3fold_page_unlock(zhdr);
         return -EAGAIN;
     }
     new_zhdr = page_address(newpage);
     memcpy(new_zhdr, zhdr, PAGE_SIZE);
     newpage->private = page->private;
     set_bit(PAGE_MIGRATED, &page->private);
     z3fold_page_unlock(zhdr);
     spin_lock_init(&new_zhdr->page_lock);
     INIT_WORK(&new_zhdr->work, compact_page_work);
     /*
      * z3fold_page_isolate() ensures that new_zhdr->buddy is empty,
      * so we only have to reinitialize it.
      */
     INIT_LIST_HEAD(&new_zhdr->buddy);
     __ClearPageMovable(page);
 
     get_page(newpage);
     z3fold_page_lock(new_zhdr);
     if (new_zhdr->first_chunks)
         encode_handle(new_zhdr, FIRST);
     if (new_zhdr->last_chunks)
         encode_handle(new_zhdr, LAST);
     if (new_zhdr->middle_chunks)
         encode_handle(new_zhdr, MIDDLE);
     set_bit(NEEDS_COMPACTING, &newpage->private);
     new_zhdr->cpu = smp_processor_id();
     spin_lock(&pool->lock);
     list_add(&newpage->lru, &pool->lru);
     spin_unlock(&pool->lock);
     __SetPageMovable(newpage, &z3fold_mops);
     z3fold_page_unlock(new_zhdr);
 
     queue_work_on(new_zhdr->cpu, pool->compact_wq, &new_zhdr->work);
 
     /* PAGE_CLAIMED and PAGE_MIGRATED are cleared now. */
     page->private = 0;
     put_page(page);
     return 0;
 }
 
 static void z3fold_page_putback(struct page *page)
 {
     struct z3fold_header *zhdr;
     struct z3fold_pool *pool;
 
     zhdr = page_address(page);
     pool = zhdr_to_pool(zhdr);
 
     z3fold_page_lock(zhdr);
     if (!list_empty(&zhdr->buddy))
         list_del_init(&zhdr->buddy);
     INIT_LIST_HEAD(&page->lru);
     if (kref_put(&zhdr->refcount, release_z3fold_page_locked))
         return;
     spin_lock(&pool->lock);
     list_add(&page->lru, &pool->lru);
     spin_unlock(&pool->lock);
     if (list_empty(&zhdr->buddy))
         add_to_unbuddied(pool, zhdr);
     clear_bit(PAGE_CLAIMED, &page->private);
     z3fold_page_unlock(zhdr);
 }
 
 static const struct movable_operations z3fold_mops = {
     .isolate_page = z3fold_page_isolate,
     .migrate_page = z3fold_page_migrate,
     .putback_page = z3fold_page_putback,
 };
 
 /*****************
  * zpool
  ****************/
 
 static int z3fold_zpool_evict(struct z3fold_pool *pool, unsigned long handle)
 {
     if (pool->zpool && pool->zpool_ops && pool->zpool_ops->evict)
         return pool->zpool_ops->evict(pool->zpool, handle);
     else
         return -ENOENT;
 }
 
 static const struct z3fold_ops z3fold_zpool_ops = {
     .evict =    z3fold_zpool_evict
 };
 
 static void *z3fold_zpool_create(const char *name, gfp_t gfp,
                    const struct zpool_ops *zpool_ops,
                    struct zpool *zpool)
 {
     struct z3fold_pool *pool;
 
     pool = z3fold_create_pool(name, gfp,
                 zpool_ops ? &z3fold_zpool_ops : NULL);
     if (pool) {
         pool->zpool = zpool;
         pool->zpool_ops = zpool_ops;
     }
     return pool;
 }
 
 static void z3fold_zpool_destroy(void *pool)
 {
     z3fold_destroy_pool(pool);
 }
 
 static int z3fold_zpool_malloc(void *pool, size_t size, gfp_t gfp,
             unsigned long *handle)
 {
     return z3fold_alloc(pool, size, gfp, handle);
 }
 static void z3fold_zpool_free(void *pool, unsigned long handle)
 {
     z3fold_free(pool, handle);
 }
 
 static int z3fold_zpool_shrink(void *pool, unsigned int pages,
             unsigned int *reclaimed)
 {
     unsigned int total = 0;
     int ret = -EINVAL;
 
     while (total < pages) {
         ret = z3fold_reclaim_page(pool, 8);
         if (ret < 0)
             break;
         total++;
     }
 
     if (reclaimed)
         *reclaimed = total;
 
     return ret;
 }
 
 static void *z3fold_zpool_map(void *pool, unsigned long handle,
             enum zpool_mapmode mm)
 {
     return z3fold_map(pool, handle);
 }
 static void z3fold_zpool_unmap(void *pool, unsigned long handle)
 {
     z3fold_unmap(pool, handle);
 }
 
 static u64 z3fold_zpool_total_size(void *pool)
 {
     return z3fold_get_pool_size(pool) * PAGE_SIZE;
 }
 
 static struct zpool_driver z3fold_zpool_driver = {
     .type =     "z3fold",
     .sleep_mapped = true,
     .owner =    THIS_MODULE,
     .create =   z3fold_zpool_create,
     .destroy =  z3fold_zpool_destroy,
     .malloc =   z3fold_zpool_malloc,
     .free =     z3fold_zpool_free,
     .shrink =   z3fold_zpool_shrink,
     .map =      z3fold_zpool_map,
     .unmap =    z3fold_zpool_unmap,
     .total_size =   z3fold_zpool_total_size,
 };
 
 MODULE_ALIAS("zpool-z3fold");
 
 static int __init init_z3fold(void)
 {
     /*
      * Make sure the z3fold header is not larger than the page size and
      * there has remaining spaces for its buddy.
      */
     BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE - CHUNK_SIZE);
     zpool_register_driver(&z3fold_zpool_driver);
 
     return 0;
 }
 
 static void __exit exit_z3fold(void)
 {
     zpool_unregister_driver(&z3fold_zpool_driver);
 }
 
 module_init(init_z3fold);
 module_exit(exit_z3fold);
 
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Vitaly Wool <vitalywool@gmail.com>");
 MODULE_DESCRIPTION("3-Fold Allocator for Compressed Pages");

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