Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1832 insertions, 0 deletions

diff --git a/mm/z3fold.c b/mm/z3fold.c
new file mode 100644
index 000000000..912ac9a64
--- /dev/null
+++ b/mm/z3fold.c
@@ -0,0 +1,1832 @@
+// 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/mount.h>
+#include <linux/pseudo_fs.h>
+#include <linux/fs.h>
+#include <linux/preempt.h>
+#include <linux/workqueue.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/zpool.h>
+#include <linux/magic.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		((PAGE_SIZE - ZHDR_SIZE_ALIGNED) >> CHUNK_SHIFT)
+
+#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.
+ * @compact_wq:	workqueue for page layout background optimization
+ * @release_wq:	workqueue for safe page release
+ * @work:	work_struct for safe page release
+ * @inode:	inode for z3fold pseudo filesystem
+ *
+ * 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;
+	struct inode *inode;
+};
+
+/*
+ * 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 */
+};
+
+/*
+ * 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;
+
+	slots = kmem_cache_zalloc(pool->c_handle,
+				 (gfp & ~(__GFP_HIGHMEM | __GFP_MOVABLE)));
+
+	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);
+}
+
+
+static inline struct z3fold_header *__get_z3fold_header(unsigned long handle,
+							bool lock)
+{
+	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);
+			if (lock)
+				locked = z3fold_page_trylock(zhdr);
+			read_unlock(&slots->lock);
+			if (locked)
+				break;
+			cpu_relax();
+		} while (lock);
+	} else {
+		zhdr = (struct z3fold_header *)(handle & PAGE_MASK);
+	}
+
+	return zhdr;
+}
+
+/* Returns the z3fold page where a given handle is stored */
+static inline struct z3fold_header *handle_to_z3fold_header(unsigned long h)
+{
+	return __get_z3fold_header(h, false);
+}
+
+/* return locked z3fold page if it's not headless */
+static inline struct z3fold_header *get_z3fold_header(unsigned long h)
+{
+	return __get_z3fold_header(h, true);
+}
+
+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 (handle & (1 << PAGE_HEADLESS))
+		return;
+
+	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);
+	}
+}
+
+static int z3fold_init_fs_context(struct fs_context *fc)
+{
+	return init_pseudo(fc, Z3FOLD_MAGIC) ? 0 : -ENOMEM;
+}
+
+static struct file_system_type z3fold_fs = {
+	.name		= "z3fold",
+	.init_fs_context = z3fold_init_fs_context,
+	.kill_sb	= kill_anon_super,
+};
+
+static struct vfsmount *z3fold_mnt;
+static int z3fold_mount(void)
+{
+	int ret = 0;
+
+	z3fold_mnt = kern_mount(&z3fold_fs);
+	if (IS_ERR(z3fold_mnt))
+		ret = PTR_ERR(z3fold_mnt);
+
+	return ret;
+}
+
+static void z3fold_unmount(void)
+{
+	kern_unmount(z3fold_mnt);
+}
+
+static const struct address_space_operations z3fold_aops;
+static int z3fold_register_migration(struct z3fold_pool *pool)
+{
+	pool->inode = alloc_anon_inode(z3fold_mnt->mnt_sb);
+	if (IS_ERR(pool->inode)) {
+		pool->inode = NULL;
+		return 1;
+	}
+
+	pool->inode->i_mapping->private_data = pool;
+	pool->inode->i_mapping->a_ops = &z3fold_aops;
+	return 0;
+}
+
+static void z3fold_unregister_migration(struct z3fold_pool *pool)
+{
+	if (pool->inode)
+		iput(pool->inode);
+ }
+
+/* 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);
+	if (headless)
+		return zhdr;
+
+	slots = alloc_slots(pool, gfp);
+	if (!slots)
+		return NULL;
+
+	spin_lock_init(&zhdr->page_lock);
+	kref_init(&zhdr->refcount);
+	zhdr->first_chunks = 0;
+	zhdr->middle_chunks = 0;
+	zhdr->last_chunks = 0;
+	zhdr->first_num = 0;
+	zhdr->start_middle = 0;
+	zhdr->cpu = -1;
+	zhdr->foreign_handles = 0;
+	zhdr->mapped_count = 0;
+	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);
+	}
+	ClearPagePrivate(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);
+}
+
+static void __attribute__((__unused__))
+			release_z3fold_page(struct kref *ref)
+{
+	struct z3fold_header *zhdr = container_of(ref, struct z3fold_header,
+						refcount);
+	__release_z3fold_page(zhdr, false);
+}
+
+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 = get_cpu_ptr(pool->unbuddied);
+
+		int freechunks = num_free_chunks(zhdr);
+		spin_lock(&pool->lock);
+		list_add(&zhdr->buddy, &unbuddied[freechunks]);
+		spin_unlock(&pool->lock);
+		zhdr->cpu = smp_processor_id();
+		put_cpu_ptr(pool->unbuddied);
+	}
+}
+
+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) {
+		if (kref_put(&new_zhdr->refcount, release_z3fold_page_locked))
+			atomic64_dec(&pool->pages_nr);
+		else {
+			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)) {
+		atomic64_dec(&pool->pages_nr);
+		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))
+			atomic64_dec(&pool->pages_nr);
+		else {
+			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:
+	/* First, try to find an unbuddied z3fold page. */
+	unbuddied = get_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);
+		l = &unbuddied[i];
+		if (unlikely(zhdr != list_first_entry(READ_ONCE(l),
+						struct z3fold_header, buddy)) ||
+		    !z3fold_page_trylock(zhdr)) {
+			spin_unlock(&pool->lock);
+			zhdr = NULL;
+			put_cpu_ptr(pool->unbuddied);
+			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;
+			put_cpu_ptr(pool->unbuddied);
+			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;
+	}
+	put_cpu_ptr(pool->unbuddied);
+
+	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,
+					can_sleep ? GFP_NOIO : GFP_ATOMIC);
+	return zhdr;
+}
+
+/*
+ * 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, 2);
+	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;
+	if (z3fold_register_migration(pool))
+		goto out_rwq;
+	INIT_WORK(&pool->work, free_pages_work);
+	pool->ops = ops;
+	return pool;
+
+out_rwq:
+	destroy_workqueue(pool->release_wq);
+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);
+	z3fold_unregister_migration(pool);
+	free_percpu(pool->unbuddied);
+	kfree(pool);
+}
+
+/**
+ * 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.
+ *
+ * gfp should not set __GFP_HIGHMEM as highmem pages cannot be used
+ * as z3fold pool pages.
+ *
+ * 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)
+		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))
+					atomic64_dec(&pool->pages_nr);
+				else
+					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 = NULL;
+	if (can_sleep) {
+		spin_lock(&pool->stale_lock);
+		zhdr = list_first_entry_or_null(&pool->stale,
+						struct z3fold_header, buddy);
+		/*
+		 * Before allocating a page, let's see if we can take one from
+		 * the stale pages list. cancel_work_sync() can sleep so we
+		 * limit this case to the contexts where we can sleep
+		 */
+		if (zhdr) {
+			list_del(&zhdr->buddy);
+			spin_unlock(&pool->stale_lock);
+			cancel_work_sync(&zhdr->work);
+			page = virt_to_page(zhdr);
+		} else {
+			spin_unlock(&pool->stale_lock);
+		}
+	}
+	if (!page)
+		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, pool->inode->i_mapping);
+		unlock_page(page);
+	} else {
+		if (trylock_page(page)) {
+			__SetPageMovable(page, pool->inode->i_mapping);
+			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 PG_reclaim flag being set, this function
+ * only sets the first|last_chunks to 0.  The page is actually freed
+ * once both 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)) {
+		atomic64_dec(&pool->pages_nr);
+		return;
+	}
+	if (page_claimed) {
+		/* the page has not been claimed by us */
+		z3fold_page_unlock(zhdr);
+		return;
+	}
+	if (test_and_set_bit(NEEDS_COMPACTING, &page->private)) {
+		put_z3fold_header(zhdr);
+		clear_bit(PAGE_CLAIMED, &page->private);
+		return;
+	}
+	if (zhdr->cpu < 0 || !cpu_online(zhdr->cpu)) {
+		spin_lock(&pool->lock);
+		list_del_init(&zhdr->buddy);
+		spin_unlock(&pool->lock);
+		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 (kref_get_unless_zero(&zhdr->refcount) == 0) {
+				zhdr = NULL;
+				break;
+			}
+			if (!z3fold_page_trylock(zhdr)) {
+				if (kref_put(&zhdr->refcount,
+						release_z3fold_page))
+					atomic64_dec(&pool->pages_nr);
+				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)) {
+				if (kref_put(&zhdr->refcount,
+						release_z3fold_page_locked))
+					atomic64_dec(&pool->pages_nr);
+				else
+					z3fold_page_unlock(zhdr);
+				zhdr = NULL;
+				continue; /* can't evict such page */
+			}
+			list_del_init(&zhdr->buddy);
+			zhdr->cpu = -1;
+			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);
+				atomic64_dec(&pool->pages_nr);
+				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);
+			z3fold_page_unlock(zhdr);
+			clear_bit(PAGE_CLAIMED, &page->private);
+		}
+
+		/* 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 address_space *mapping, struct page *newpage,
+			       struct page *page, enum migrate_mode mode)
+{
+	struct z3fold_header *zhdr, *new_zhdr;
+	struct z3fold_pool *pool;
+	struct address_space *new_mapping;
+
+	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) {
+		z3fold_page_unlock(zhdr);
+		clear_bit(PAGE_CLAIMED, &page->private);
+		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;
+	page->private = 0;
+	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);
+	new_mapping = page_mapping(page);
+	__ClearPageMovable(page);
+	ClearPagePrivate(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, new_mapping);
+	z3fold_page_unlock(new_zhdr);
+
+	queue_work_on(new_zhdr->cpu, pool->compact_wq, &new_zhdr->work);
+
+	page_mapcount_reset(page);
+	clear_bit(PAGE_CLAIMED, &page->private);
+	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)) {
+		atomic64_dec(&pool->pages_nr);
+		return;
+	}
+	spin_lock(&pool->lock);
+	list_add(&page->lru, &pool->lru);
+	spin_unlock(&pool->lock);
+	clear_bit(PAGE_CLAIMED, &page->private);
+	z3fold_page_unlock(zhdr);
+}
+
+static const struct address_space_operations z3fold_aops = {
+	.isolate_page = z3fold_page_isolate,
+	.migratepage = 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",
+	.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)
+{
+	int ret;
+
+	/* Make sure the z3fold header is not larger than the page size */
+	BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE);
+	ret = z3fold_mount();
+	if (ret)
+		return ret;
+
+	zpool_register_driver(&z3fold_zpool_driver);
+
+	return 0;
+}
+
+static void __exit exit_z3fold(void)
+{
+	z3fold_unmount();
+	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");