Adding upstream version 5.10.209.upstream/5.10.209upstream

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

1 files changed, 2581 insertions, 0 deletions

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
new file mode 100644
index 000000000..c18dc8e61
--- /dev/null
+++ b/mm/zsmalloc.c
@@ -0,0 +1,2581 @@
+/*
+ * zsmalloc memory allocator
+ *
+ * Copyright (C) 2011  Nitin Gupta
+ * Copyright (C) 2012, 2013 Minchan Kim
+ *
+ * This code is released using a dual license strategy: BSD/GPL
+ * You can choose the license that better fits your requirements.
+ *
+ * Released under the terms of 3-clause BSD License
+ * Released under the terms of GNU General Public License Version 2.0
+ */
+
+/*
+ * Following is how we use various fields and flags of underlying
+ * struct page(s) to form a zspage.
+ *
+ * Usage of struct page fields:
+ *	page->private: points to zspage
+ *	page->freelist(index): links together all component pages of a zspage
+ *		For the huge page, this is always 0, so we use this field
+ *		to store handle.
+ *	page->units: first object offset in a subpage of zspage
+ *
+ * Usage of struct page flags:
+ *	PG_private: identifies the first component page
+ *	PG_owner_priv_1: identifies the huge component page
+ *
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/magic.h>
+#include <linux/bitops.h>
+#include <linux/errno.h>
+#include <linux/highmem.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/pgtable.h>
+#include <asm/tlbflush.h>
+#include <linux/cpumask.h>
+#include <linux/cpu.h>
+#include <linux/vmalloc.h>
+#include <linux/preempt.h>
+#include <linux/spinlock.h>
+#include <linux/shrinker.h>
+#include <linux/types.h>
+#include <linux/debugfs.h>
+#include <linux/zsmalloc.h>
+#include <linux/zpool.h>
+#include <linux/mount.h>
+#include <linux/pseudo_fs.h>
+#include <linux/migrate.h>
+#include <linux/wait.h>
+#include <linux/pagemap.h>
+#include <linux/fs.h>
+
+#define ZSPAGE_MAGIC	0x58
+
+/*
+ * This must be power of 2 and greater than of equal to sizeof(link_free).
+ * These two conditions ensure that any 'struct link_free' itself doesn't
+ * span more than 1 page which avoids complex case of mapping 2 pages simply
+ * to restore link_free pointer values.
+ */
+#define ZS_ALIGN		8
+
+/*
+ * A single 'zspage' is composed of up to 2^N discontiguous 0-order (single)
+ * pages. ZS_MAX_ZSPAGE_ORDER defines upper limit on N.
+ */
+#define ZS_MAX_ZSPAGE_ORDER 2
+#define ZS_MAX_PAGES_PER_ZSPAGE (_AC(1, UL) << ZS_MAX_ZSPAGE_ORDER)
+
+#define ZS_HANDLE_SIZE (sizeof(unsigned long))
+
+/*
+ * Object location (<PFN>, <obj_idx>) is encoded as
+ * a single (unsigned long) handle value.
+ *
+ * Note that object index <obj_idx> starts from 0.
+ *
+ * This is made more complicated by various memory models and PAE.
+ */
+
+#ifndef MAX_POSSIBLE_PHYSMEM_BITS
+#ifdef MAX_PHYSMEM_BITS
+#define MAX_POSSIBLE_PHYSMEM_BITS MAX_PHYSMEM_BITS
+#else
+/*
+ * If this definition of MAX_PHYSMEM_BITS is used, OBJ_INDEX_BITS will just
+ * be PAGE_SHIFT
+ */
+#define MAX_POSSIBLE_PHYSMEM_BITS BITS_PER_LONG
+#endif
+#endif
+
+#define _PFN_BITS		(MAX_POSSIBLE_PHYSMEM_BITS - PAGE_SHIFT)
+
+/*
+ * Memory for allocating for handle keeps object position by
+ * encoding <page, obj_idx> and the encoded value has a room
+ * in least bit(ie, look at obj_to_location).
+ * We use the bit to synchronize between object access by
+ * user and migration.
+ */
+#define HANDLE_PIN_BIT	0
+
+/*
+ * Head in allocated object should have OBJ_ALLOCATED_TAG
+ * to identify the object was allocated or not.
+ * It's okay to add the status bit in the least bit because
+ * header keeps handle which is 4byte-aligned address so we
+ * have room for two bit at least.
+ */
+#define OBJ_ALLOCATED_TAG 1
+#define OBJ_TAG_BITS 1
+#define OBJ_INDEX_BITS	(BITS_PER_LONG - _PFN_BITS - OBJ_TAG_BITS)
+#define OBJ_INDEX_MASK	((_AC(1, UL) << OBJ_INDEX_BITS) - 1)
+
+#define FULLNESS_BITS	2
+#define CLASS_BITS	8
+#define ISOLATED_BITS	3
+#define MAGIC_VAL_BITS	8
+
+#define MAX(a, b) ((a) >= (b) ? (a) : (b))
+/* ZS_MIN_ALLOC_SIZE must be multiple of ZS_ALIGN */
+#define ZS_MIN_ALLOC_SIZE \
+	MAX(32, (ZS_MAX_PAGES_PER_ZSPAGE << PAGE_SHIFT >> OBJ_INDEX_BITS))
+/* each chunk includes extra space to keep handle */
+#define ZS_MAX_ALLOC_SIZE	PAGE_SIZE
+
+/*
+ * On systems with 4K page size, this gives 255 size classes! There is a
+ * trader-off here:
+ *  - Large number of size classes is potentially wasteful as free page are
+ *    spread across these classes
+ *  - Small number of size classes causes large internal fragmentation
+ *  - Probably its better to use specific size classes (empirically
+ *    determined). NOTE: all those class sizes must be set as multiple of
+ *    ZS_ALIGN to make sure link_free itself never has to span 2 pages.
+ *
+ *  ZS_MIN_ALLOC_SIZE and ZS_SIZE_CLASS_DELTA must be multiple of ZS_ALIGN
+ *  (reason above)
+ */
+#define ZS_SIZE_CLASS_DELTA	(PAGE_SIZE >> CLASS_BITS)
+#define ZS_SIZE_CLASSES	(DIV_ROUND_UP(ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE, \
+				      ZS_SIZE_CLASS_DELTA) + 1)
+
+enum fullness_group {
+	ZS_EMPTY,
+	ZS_ALMOST_EMPTY,
+	ZS_ALMOST_FULL,
+	ZS_FULL,
+	NR_ZS_FULLNESS,
+};
+
+enum zs_stat_type {
+	CLASS_EMPTY,
+	CLASS_ALMOST_EMPTY,
+	CLASS_ALMOST_FULL,
+	CLASS_FULL,
+	OBJ_ALLOCATED,
+	OBJ_USED,
+	NR_ZS_STAT_TYPE,
+};
+
+struct zs_size_stat {
+	unsigned long objs[NR_ZS_STAT_TYPE];
+};
+
+#ifdef CONFIG_ZSMALLOC_STAT
+static struct dentry *zs_stat_root;
+#endif
+
+#ifdef CONFIG_COMPACTION
+static struct vfsmount *zsmalloc_mnt;
+#endif
+
+/*
+ * We assign a page to ZS_ALMOST_EMPTY fullness group when:
+ *	n <= N / f, where
+ * n = number of allocated objects
+ * N = total number of objects zspage can store
+ * f = fullness_threshold_frac
+ *
+ * Similarly, we assign zspage to:
+ *	ZS_ALMOST_FULL	when n > N / f
+ *	ZS_EMPTY	when n == 0
+ *	ZS_FULL		when n == N
+ *
+ * (see: fix_fullness_group())
+ */
+static const int fullness_threshold_frac = 4;
+static size_t huge_class_size;
+
+struct size_class {
+	spinlock_t lock;
+	struct list_head fullness_list[NR_ZS_FULLNESS];
+	/*
+	 * Size of objects stored in this class. Must be multiple
+	 * of ZS_ALIGN.
+	 */
+	int size;
+	int objs_per_zspage;
+	/* Number of PAGE_SIZE sized pages to combine to form a 'zspage' */
+	int pages_per_zspage;
+
+	unsigned int index;
+	struct zs_size_stat stats;
+};
+
+/* huge object: pages_per_zspage == 1 && maxobj_per_zspage == 1 */
+static void SetPageHugeObject(struct page *page)
+{
+	SetPageOwnerPriv1(page);
+}
+
+static void ClearPageHugeObject(struct page *page)
+{
+	ClearPageOwnerPriv1(page);
+}
+
+static int PageHugeObject(struct page *page)
+{
+	return PageOwnerPriv1(page);
+}
+
+/*
+ * Placed within free objects to form a singly linked list.
+ * For every zspage, zspage->freeobj gives head of this list.
+ *
+ * This must be power of 2 and less than or equal to ZS_ALIGN
+ */
+struct link_free {
+	union {
+		/*
+		 * Free object index;
+		 * It's valid for non-allocated object
+		 */
+		unsigned long next;
+		/*
+		 * Handle of allocated object.
+		 */
+		unsigned long handle;
+	};
+};
+
+struct zs_pool {
+	const char *name;
+
+	struct size_class *size_class[ZS_SIZE_CLASSES];
+	struct kmem_cache *handle_cachep;
+	struct kmem_cache *zspage_cachep;
+
+	atomic_long_t pages_allocated;
+
+	struct zs_pool_stats stats;
+
+	/* Compact classes */
+	struct shrinker shrinker;
+
+#ifdef CONFIG_ZSMALLOC_STAT
+	struct dentry *stat_dentry;
+#endif
+#ifdef CONFIG_COMPACTION
+	struct inode *inode;
+	struct work_struct free_work;
+	/* A wait queue for when migration races with async_free_zspage() */
+	struct wait_queue_head migration_wait;
+	atomic_long_t isolated_pages;
+	bool destroying;
+#endif
+};
+
+struct zspage {
+	struct {
+		unsigned int fullness:FULLNESS_BITS;
+		unsigned int class:CLASS_BITS + 1;
+		unsigned int isolated:ISOLATED_BITS;
+		unsigned int magic:MAGIC_VAL_BITS;
+	};
+	unsigned int inuse;
+	unsigned int freeobj;
+	struct page *first_page;
+	struct list_head list; /* fullness list */
+#ifdef CONFIG_COMPACTION
+	rwlock_t lock;
+#endif
+};
+
+struct mapping_area {
+	char *vm_buf; /* copy buffer for objects that span pages */
+	char *vm_addr; /* address of kmap_atomic()'ed pages */
+	enum zs_mapmode vm_mm; /* mapping mode */
+};
+
+#ifdef CONFIG_COMPACTION
+static int zs_register_migration(struct zs_pool *pool);
+static void zs_unregister_migration(struct zs_pool *pool);
+static void migrate_lock_init(struct zspage *zspage);
+static void migrate_read_lock(struct zspage *zspage);
+static void migrate_read_unlock(struct zspage *zspage);
+static void kick_deferred_free(struct zs_pool *pool);
+static void init_deferred_free(struct zs_pool *pool);
+static void SetZsPageMovable(struct zs_pool *pool, struct zspage *zspage);
+#else
+static int zsmalloc_mount(void) { return 0; }
+static void zsmalloc_unmount(void) {}
+static int zs_register_migration(struct zs_pool *pool) { return 0; }
+static void zs_unregister_migration(struct zs_pool *pool) {}
+static void migrate_lock_init(struct zspage *zspage) {}
+static void migrate_read_lock(struct zspage *zspage) {}
+static void migrate_read_unlock(struct zspage *zspage) {}
+static void kick_deferred_free(struct zs_pool *pool) {}
+static void init_deferred_free(struct zs_pool *pool) {}
+static void SetZsPageMovable(struct zs_pool *pool, struct zspage *zspage) {}
+#endif
+
+static int create_cache(struct zs_pool *pool)
+{
+	pool->handle_cachep = kmem_cache_create("zs_handle", ZS_HANDLE_SIZE,
+					0, 0, NULL);
+	if (!pool->handle_cachep)
+		return 1;
+
+	pool->zspage_cachep = kmem_cache_create("zspage", sizeof(struct zspage),
+					0, 0, NULL);
+	if (!pool->zspage_cachep) {
+		kmem_cache_destroy(pool->handle_cachep);
+		pool->handle_cachep = NULL;
+		return 1;
+	}
+
+	return 0;
+}
+
+static void destroy_cache(struct zs_pool *pool)
+{
+	kmem_cache_destroy(pool->handle_cachep);
+	kmem_cache_destroy(pool->zspage_cachep);
+}
+
+static unsigned long cache_alloc_handle(struct zs_pool *pool, gfp_t gfp)
+{
+	return (unsigned long)kmem_cache_alloc(pool->handle_cachep,
+			gfp & ~(__GFP_HIGHMEM|__GFP_MOVABLE));
+}
+
+static void cache_free_handle(struct zs_pool *pool, unsigned long handle)
+{
+	kmem_cache_free(pool->handle_cachep, (void *)handle);
+}
+
+static struct zspage *cache_alloc_zspage(struct zs_pool *pool, gfp_t flags)
+{
+	return kmem_cache_alloc(pool->zspage_cachep,
+			flags & ~(__GFP_HIGHMEM|__GFP_MOVABLE));
+}
+
+static void cache_free_zspage(struct zs_pool *pool, struct zspage *zspage)
+{
+	kmem_cache_free(pool->zspage_cachep, zspage);
+}
+
+static void record_obj(unsigned long handle, unsigned long obj)
+{
+	/*
+	 * lsb of @obj represents handle lock while other bits
+	 * represent object value the handle is pointing so
+	 * updating shouldn't do store tearing.
+	 */
+	WRITE_ONCE(*(unsigned long *)handle, obj);
+}
+
+/* zpool driver */
+
+#ifdef CONFIG_ZPOOL
+
+static void *zs_zpool_create(const char *name, gfp_t gfp,
+			     const struct zpool_ops *zpool_ops,
+			     struct zpool *zpool)
+{
+	/*
+	 * Ignore global gfp flags: zs_malloc() may be invoked from
+	 * different contexts and its caller must provide a valid
+	 * gfp mask.
+	 */
+	return zs_create_pool(name);
+}
+
+static void zs_zpool_destroy(void *pool)
+{
+	zs_destroy_pool(pool);
+}
+
+static int zs_zpool_malloc(void *pool, size_t size, gfp_t gfp,
+			unsigned long *handle)
+{
+	*handle = zs_malloc(pool, size, gfp);
+	return *handle ? 0 : -1;
+}
+static void zs_zpool_free(void *pool, unsigned long handle)
+{
+	zs_free(pool, handle);
+}
+
+static void *zs_zpool_map(void *pool, unsigned long handle,
+			enum zpool_mapmode mm)
+{
+	enum zs_mapmode zs_mm;
+
+	switch (mm) {
+	case ZPOOL_MM_RO:
+		zs_mm = ZS_MM_RO;
+		break;
+	case ZPOOL_MM_WO:
+		zs_mm = ZS_MM_WO;
+		break;
+	case ZPOOL_MM_RW:
+	default:
+		zs_mm = ZS_MM_RW;
+		break;
+	}
+
+	return zs_map_object(pool, handle, zs_mm);
+}
+static void zs_zpool_unmap(void *pool, unsigned long handle)
+{
+	zs_unmap_object(pool, handle);
+}
+
+static u64 zs_zpool_total_size(void *pool)
+{
+	return zs_get_total_pages(pool) << PAGE_SHIFT;
+}
+
+static struct zpool_driver zs_zpool_driver = {
+	.type =			  "zsmalloc",
+	.owner =		  THIS_MODULE,
+	.create =		  zs_zpool_create,
+	.destroy =		  zs_zpool_destroy,
+	.malloc_support_movable = true,
+	.malloc =		  zs_zpool_malloc,
+	.free =			  zs_zpool_free,
+	.map =			  zs_zpool_map,
+	.unmap =		  zs_zpool_unmap,
+	.total_size =		  zs_zpool_total_size,
+};
+
+MODULE_ALIAS("zpool-zsmalloc");
+#endif /* CONFIG_ZPOOL */
+
+/* per-cpu VM mapping areas for zspage accesses that cross page boundaries */
+static DEFINE_PER_CPU(struct mapping_area, zs_map_area);
+
+static bool is_zspage_isolated(struct zspage *zspage)
+{
+	return zspage->isolated;
+}
+
+static __maybe_unused int is_first_page(struct page *page)
+{
+	return PagePrivate(page);
+}
+
+/* Protected by class->lock */
+static inline int get_zspage_inuse(struct zspage *zspage)
+{
+	return zspage->inuse;
+}
+
+
+static inline void mod_zspage_inuse(struct zspage *zspage, int val)
+{
+	zspage->inuse += val;
+}
+
+static inline struct page *get_first_page(struct zspage *zspage)
+{
+	struct page *first_page = zspage->first_page;
+
+	VM_BUG_ON_PAGE(!is_first_page(first_page), first_page);
+	return first_page;
+}
+
+static inline int get_first_obj_offset(struct page *page)
+{
+	return page->units;
+}
+
+static inline void set_first_obj_offset(struct page *page, int offset)
+{
+	page->units = offset;
+}
+
+static inline unsigned int get_freeobj(struct zspage *zspage)
+{
+	return zspage->freeobj;
+}
+
+static inline void set_freeobj(struct zspage *zspage, unsigned int obj)
+{
+	zspage->freeobj = obj;
+}
+
+static void get_zspage_mapping(struct zspage *zspage,
+				unsigned int *class_idx,
+				enum fullness_group *fullness)
+{
+	BUG_ON(zspage->magic != ZSPAGE_MAGIC);
+
+	*fullness = zspage->fullness;
+	*class_idx = zspage->class;
+}
+
+static void set_zspage_mapping(struct zspage *zspage,
+				unsigned int class_idx,
+				enum fullness_group fullness)
+{
+	zspage->class = class_idx;
+	zspage->fullness = fullness;
+}
+
+/*
+ * zsmalloc divides the pool into various size classes where each
+ * class maintains a list of zspages where each zspage is divided
+ * into equal sized chunks. Each allocation falls into one of these
+ * classes depending on its size. This function returns index of the
+ * size class which has chunk size big enough to hold the give size.
+ */
+static int get_size_class_index(int size)
+{
+	int idx = 0;
+
+	if (likely(size > ZS_MIN_ALLOC_SIZE))
+		idx = DIV_ROUND_UP(size - ZS_MIN_ALLOC_SIZE,
+				ZS_SIZE_CLASS_DELTA);
+
+	return min_t(int, ZS_SIZE_CLASSES - 1, idx);
+}
+
+/* type can be of enum type zs_stat_type or fullness_group */
+static inline void zs_stat_inc(struct size_class *class,
+				int type, unsigned long cnt)
+{
+	class->stats.objs[type] += cnt;
+}
+
+/* type can be of enum type zs_stat_type or fullness_group */
+static inline void zs_stat_dec(struct size_class *class,
+				int type, unsigned long cnt)
+{
+	class->stats.objs[type] -= cnt;
+}
+
+/* type can be of enum type zs_stat_type or fullness_group */
+static inline unsigned long zs_stat_get(struct size_class *class,
+				int type)
+{
+	return class->stats.objs[type];
+}
+
+#ifdef CONFIG_ZSMALLOC_STAT
+
+static void __init zs_stat_init(void)
+{
+	if (!debugfs_initialized()) {
+		pr_warn("debugfs not available, stat dir not created\n");
+		return;
+	}
+
+	zs_stat_root = debugfs_create_dir("zsmalloc", NULL);
+}
+
+static void __exit zs_stat_exit(void)
+{
+	debugfs_remove_recursive(zs_stat_root);
+}
+
+static unsigned long zs_can_compact(struct size_class *class);
+
+static int zs_stats_size_show(struct seq_file *s, void *v)
+{
+	int i;
+	struct zs_pool *pool = s->private;
+	struct size_class *class;
+	int objs_per_zspage;
+	unsigned long class_almost_full, class_almost_empty;
+	unsigned long obj_allocated, obj_used, pages_used, freeable;
+	unsigned long total_class_almost_full = 0, total_class_almost_empty = 0;
+	unsigned long total_objs = 0, total_used_objs = 0, total_pages = 0;
+	unsigned long total_freeable = 0;
+
+	seq_printf(s, " %5s %5s %11s %12s %13s %10s %10s %16s %8s\n",
+			"class", "size", "almost_full", "almost_empty",
+			"obj_allocated", "obj_used", "pages_used",
+			"pages_per_zspage", "freeable");
+
+	for (i = 0; i < ZS_SIZE_CLASSES; i++) {
+		class = pool->size_class[i];
+
+		if (class->index != i)
+			continue;
+
+		spin_lock(&class->lock);
+		class_almost_full = zs_stat_get(class, CLASS_ALMOST_FULL);
+		class_almost_empty = zs_stat_get(class, CLASS_ALMOST_EMPTY);
+		obj_allocated = zs_stat_get(class, OBJ_ALLOCATED);
+		obj_used = zs_stat_get(class, OBJ_USED);
+		freeable = zs_can_compact(class);
+		spin_unlock(&class->lock);
+
+		objs_per_zspage = class->objs_per_zspage;
+		pages_used = obj_allocated / objs_per_zspage *
+				class->pages_per_zspage;
+
+		seq_printf(s, " %5u %5u %11lu %12lu %13lu"
+				" %10lu %10lu %16d %8lu\n",
+			i, class->size, class_almost_full, class_almost_empty,
+			obj_allocated, obj_used, pages_used,
+			class->pages_per_zspage, freeable);
+
+		total_class_almost_full += class_almost_full;
+		total_class_almost_empty += class_almost_empty;
+		total_objs += obj_allocated;
+		total_used_objs += obj_used;
+		total_pages += pages_used;
+		total_freeable += freeable;
+	}
+
+	seq_puts(s, "\n");
+	seq_printf(s, " %5s %5s %11lu %12lu %13lu %10lu %10lu %16s %8lu\n",
+			"Total", "", total_class_almost_full,
+			total_class_almost_empty, total_objs,
+			total_used_objs, total_pages, "", total_freeable);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(zs_stats_size);
+
+static void zs_pool_stat_create(struct zs_pool *pool, const char *name)
+{
+	if (!zs_stat_root) {
+		pr_warn("no root stat dir, not creating <%s> stat dir\n", name);
+		return;
+	}
+
+	pool->stat_dentry = debugfs_create_dir(name, zs_stat_root);
+
+	debugfs_create_file("classes", S_IFREG | 0444, pool->stat_dentry, pool,
+			    &zs_stats_size_fops);
+}
+
+static void zs_pool_stat_destroy(struct zs_pool *pool)
+{
+	debugfs_remove_recursive(pool->stat_dentry);
+}
+
+#else /* CONFIG_ZSMALLOC_STAT */
+static void __init zs_stat_init(void)
+{
+}
+
+static void __exit zs_stat_exit(void)
+{
+}
+
+static inline void zs_pool_stat_create(struct zs_pool *pool, const char *name)
+{
+}
+
+static inline void zs_pool_stat_destroy(struct zs_pool *pool)
+{
+}
+#endif
+
+
+/*
+ * For each size class, zspages are divided into different groups
+ * depending on how "full" they are. This was done so that we could
+ * easily find empty or nearly empty zspages when we try to shrink
+ * the pool (not yet implemented). This function returns fullness
+ * status of the given page.
+ */
+static enum fullness_group get_fullness_group(struct size_class *class,
+						struct zspage *zspage)
+{
+	int inuse, objs_per_zspage;
+	enum fullness_group fg;
+
+	inuse = get_zspage_inuse(zspage);
+	objs_per_zspage = class->objs_per_zspage;
+
+	if (inuse == 0)
+		fg = ZS_EMPTY;
+	else if (inuse == objs_per_zspage)
+		fg = ZS_FULL;
+	else if (inuse <= 3 * objs_per_zspage / fullness_threshold_frac)
+		fg = ZS_ALMOST_EMPTY;
+	else
+		fg = ZS_ALMOST_FULL;
+
+	return fg;
+}
+
+/*
+ * Each size class maintains various freelists and zspages are assigned
+ * to one of these freelists based on the number of live objects they
+ * have. This functions inserts the given zspage into the freelist
+ * identified by <class, fullness_group>.
+ */
+static void insert_zspage(struct size_class *class,
+				struct zspage *zspage,
+				enum fullness_group fullness)
+{
+	struct zspage *head;
+
+	zs_stat_inc(class, fullness, 1);
+	head = list_first_entry_or_null(&class->fullness_list[fullness],
+					struct zspage, list);
+	/*
+	 * We want to see more ZS_FULL pages and less almost empty/full.
+	 * Put pages with higher ->inuse first.
+	 */
+	if (head) {
+		if (get_zspage_inuse(zspage) < get_zspage_inuse(head)) {
+			list_add(&zspage->list, &head->list);
+			return;
+		}
+	}
+	list_add(&zspage->list, &class->fullness_list[fullness]);
+}
+
+/*
+ * This function removes the given zspage from the freelist identified
+ * by <class, fullness_group>.
+ */
+static void remove_zspage(struct size_class *class,
+				struct zspage *zspage,
+				enum fullness_group fullness)
+{
+	VM_BUG_ON(list_empty(&class->fullness_list[fullness]));
+	VM_BUG_ON(is_zspage_isolated(zspage));
+
+	list_del_init(&zspage->list);
+	zs_stat_dec(class, fullness, 1);
+}
+
+/*
+ * Each size class maintains zspages in different fullness groups depending
+ * on the number of live objects they contain. When allocating or freeing
+ * objects, the fullness status of the page can change, say, from ALMOST_FULL
+ * to ALMOST_EMPTY when freeing an object. This function checks if such
+ * a status change has occurred for the given page and accordingly moves the
+ * page from the freelist of the old fullness group to that of the new
+ * fullness group.
+ */
+static enum fullness_group fix_fullness_group(struct size_class *class,
+						struct zspage *zspage)
+{
+	int class_idx;
+	enum fullness_group currfg, newfg;
+
+	get_zspage_mapping(zspage, &class_idx, &currfg);
+	newfg = get_fullness_group(class, zspage);
+	if (newfg == currfg)
+		goto out;
+
+	if (!is_zspage_isolated(zspage)) {
+		remove_zspage(class, zspage, currfg);
+		insert_zspage(class, zspage, newfg);
+	}
+
+	set_zspage_mapping(zspage, class_idx, newfg);
+
+out:
+	return newfg;
+}
+
+/*
+ * We have to decide on how many pages to link together
+ * to form a zspage for each size class. This is important
+ * to reduce wastage due to unusable space left at end of
+ * each zspage which is given as:
+ *     wastage = Zp % class_size
+ *     usage = Zp - wastage
+ * where Zp = zspage size = k * PAGE_SIZE where k = 1, 2, ...
+ *
+ * For example, for size class of 3/8 * PAGE_SIZE, we should
+ * link together 3 PAGE_SIZE sized pages to form a zspage
+ * since then we can perfectly fit in 8 such objects.
+ */
+static int get_pages_per_zspage(int class_size)
+{
+	int i, max_usedpc = 0;
+	/* zspage order which gives maximum used size per KB */
+	int max_usedpc_order = 1;
+
+	for (i = 1; i <= ZS_MAX_PAGES_PER_ZSPAGE; i++) {
+		int zspage_size;
+		int waste, usedpc;
+
+		zspage_size = i * PAGE_SIZE;
+		waste = zspage_size % class_size;
+		usedpc = (zspage_size - waste) * 100 / zspage_size;
+
+		if (usedpc > max_usedpc) {
+			max_usedpc = usedpc;
+			max_usedpc_order = i;
+		}
+	}
+
+	return max_usedpc_order;
+}
+
+static struct zspage *get_zspage(struct page *page)
+{
+	struct zspage *zspage = (struct zspage *)page->private;
+
+	BUG_ON(zspage->magic != ZSPAGE_MAGIC);
+	return zspage;
+}
+
+static struct page *get_next_page(struct page *page)
+{
+	if (unlikely(PageHugeObject(page)))
+		return NULL;
+
+	return page->freelist;
+}
+
+/**
+ * obj_to_location - get (<page>, <obj_idx>) from encoded object value
+ * @obj: the encoded object value
+ * @page: page object resides in zspage
+ * @obj_idx: object index
+ */
+static void obj_to_location(unsigned long obj, struct page **page,
+				unsigned int *obj_idx)
+{
+	obj >>= OBJ_TAG_BITS;
+	*page = pfn_to_page(obj >> OBJ_INDEX_BITS);
+	*obj_idx = (obj & OBJ_INDEX_MASK);
+}
+
+/**
+ * location_to_obj - get obj value encoded from (<page>, <obj_idx>)
+ * @page: page object resides in zspage
+ * @obj_idx: object index
+ */
+static unsigned long location_to_obj(struct page *page, unsigned int obj_idx)
+{
+	unsigned long obj;
+
+	obj = page_to_pfn(page) << OBJ_INDEX_BITS;
+	obj |= obj_idx & OBJ_INDEX_MASK;
+	obj <<= OBJ_TAG_BITS;
+
+	return obj;
+}
+
+static unsigned long handle_to_obj(unsigned long handle)
+{
+	return *(unsigned long *)handle;
+}
+
+static unsigned long obj_to_head(struct page *page, void *obj)
+{
+	if (unlikely(PageHugeObject(page))) {
+		VM_BUG_ON_PAGE(!is_first_page(page), page);
+		return page->index;
+	} else
+		return *(unsigned long *)obj;
+}
+
+static inline int testpin_tag(unsigned long handle)
+{
+	return bit_spin_is_locked(HANDLE_PIN_BIT, (unsigned long *)handle);
+}
+
+static inline int trypin_tag(unsigned long handle)
+{
+	return bit_spin_trylock(HANDLE_PIN_BIT, (unsigned long *)handle);
+}
+
+static void pin_tag(unsigned long handle) __acquires(bitlock)
+{
+	bit_spin_lock(HANDLE_PIN_BIT, (unsigned long *)handle);
+}
+
+static void unpin_tag(unsigned long handle) __releases(bitlock)
+{
+	bit_spin_unlock(HANDLE_PIN_BIT, (unsigned long *)handle);
+}
+
+static void reset_page(struct page *page)
+{
+	__ClearPageMovable(page);
+	ClearPagePrivate(page);
+	set_page_private(page, 0);
+	page_mapcount_reset(page);
+	ClearPageHugeObject(page);
+	page->freelist = NULL;
+}
+
+static int trylock_zspage(struct zspage *zspage)
+{
+	struct page *cursor, *fail;
+
+	for (cursor = get_first_page(zspage); cursor != NULL; cursor =
+					get_next_page(cursor)) {
+		if (!trylock_page(cursor)) {
+			fail = cursor;
+			goto unlock;
+		}
+	}
+
+	return 1;
+unlock:
+	for (cursor = get_first_page(zspage); cursor != fail; cursor =
+					get_next_page(cursor))
+		unlock_page(cursor);
+
+	return 0;
+}
+
+static void __free_zspage(struct zs_pool *pool, struct size_class *class,
+				struct zspage *zspage)
+{
+	struct page *page, *next;
+	enum fullness_group fg;
+	unsigned int class_idx;
+
+	get_zspage_mapping(zspage, &class_idx, &fg);
+
+	assert_spin_locked(&class->lock);
+
+	VM_BUG_ON(get_zspage_inuse(zspage));
+	VM_BUG_ON(fg != ZS_EMPTY);
+
+	next = page = get_first_page(zspage);
+	do {
+		VM_BUG_ON_PAGE(!PageLocked(page), page);
+		next = get_next_page(page);
+		reset_page(page);
+		unlock_page(page);
+		dec_zone_page_state(page, NR_ZSPAGES);
+		put_page(page);
+		page = next;
+	} while (page != NULL);
+
+	cache_free_zspage(pool, zspage);
+
+	zs_stat_dec(class, OBJ_ALLOCATED, class->objs_per_zspage);
+	atomic_long_sub(class->pages_per_zspage,
+					&pool->pages_allocated);
+}
+
+static void free_zspage(struct zs_pool *pool, struct size_class *class,
+				struct zspage *zspage)
+{
+	VM_BUG_ON(get_zspage_inuse(zspage));
+	VM_BUG_ON(list_empty(&zspage->list));
+
+	if (!trylock_zspage(zspage)) {
+		kick_deferred_free(pool);
+		return;
+	}
+
+	remove_zspage(class, zspage, ZS_EMPTY);
+	__free_zspage(pool, class, zspage);
+}
+
+/* Initialize a newly allocated zspage */
+static void init_zspage(struct size_class *class, struct zspage *zspage)
+{
+	unsigned int freeobj = 1;
+	unsigned long off = 0;
+	struct page *page = get_first_page(zspage);
+
+	while (page) {
+		struct page *next_page;
+		struct link_free *link;
+		void *vaddr;
+
+		set_first_obj_offset(page, off);
+
+		vaddr = kmap_atomic(page);
+		link = (struct link_free *)vaddr + off / sizeof(*link);
+
+		while ((off += class->size) < PAGE_SIZE) {
+			link->next = freeobj++ << OBJ_TAG_BITS;
+			link += class->size / sizeof(*link);
+		}
+
+		/*
+		 * We now come to the last (full or partial) object on this
+		 * page, which must point to the first object on the next
+		 * page (if present)
+		 */
+		next_page = get_next_page(page);
+		if (next_page) {
+			link->next = freeobj++ << OBJ_TAG_BITS;
+		} else {
+			/*
+			 * Reset OBJ_TAG_BITS bit to last link to tell
+			 * whether it's allocated object or not.
+			 */
+			link->next = -1UL << OBJ_TAG_BITS;
+		}
+		kunmap_atomic(vaddr);
+		page = next_page;
+		off %= PAGE_SIZE;
+	}
+
+	set_freeobj(zspage, 0);
+}
+
+static void create_page_chain(struct size_class *class, struct zspage *zspage,
+				struct page *pages[])
+{
+	int i;
+	struct page *page;
+	struct page *prev_page = NULL;
+	int nr_pages = class->pages_per_zspage;
+
+	/*
+	 * Allocate individual pages and link them together as:
+	 * 1. all pages are linked together using page->freelist
+	 * 2. each sub-page point to zspage using page->private
+	 *
+	 * we set PG_private to identify the first page (i.e. no other sub-page
+	 * has this flag set).
+	 */
+	for (i = 0; i < nr_pages; i++) {
+		page = pages[i];
+		set_page_private(page, (unsigned long)zspage);
+		page->freelist = NULL;
+		if (i == 0) {
+			zspage->first_page = page;
+			SetPagePrivate(page);
+			if (unlikely(class->objs_per_zspage == 1 &&
+					class->pages_per_zspage == 1))
+				SetPageHugeObject(page);
+		} else {
+			prev_page->freelist = page;
+		}
+		prev_page = page;
+	}
+}
+
+/*
+ * Allocate a zspage for the given size class
+ */
+static struct zspage *alloc_zspage(struct zs_pool *pool,
+					struct size_class *class,
+					gfp_t gfp)
+{
+	int i;
+	struct page *pages[ZS_MAX_PAGES_PER_ZSPAGE];
+	struct zspage *zspage = cache_alloc_zspage(pool, gfp);
+
+	if (!zspage)
+		return NULL;
+
+	memset(zspage, 0, sizeof(struct zspage));
+	zspage->magic = ZSPAGE_MAGIC;
+	migrate_lock_init(zspage);
+
+	for (i = 0; i < class->pages_per_zspage; i++) {
+		struct page *page;
+
+		page = alloc_page(gfp);
+		if (!page) {
+			while (--i >= 0) {
+				dec_zone_page_state(pages[i], NR_ZSPAGES);
+				__free_page(pages[i]);
+			}
+			cache_free_zspage(pool, zspage);
+			return NULL;
+		}
+
+		inc_zone_page_state(page, NR_ZSPAGES);
+		pages[i] = page;
+	}
+
+	create_page_chain(class, zspage, pages);
+	init_zspage(class, zspage);
+
+	return zspage;
+}
+
+static struct zspage *find_get_zspage(struct size_class *class)
+{
+	int i;
+	struct zspage *zspage;
+
+	for (i = ZS_ALMOST_FULL; i >= ZS_EMPTY; i--) {
+		zspage = list_first_entry_or_null(&class->fullness_list[i],
+				struct zspage, list);
+		if (zspage)
+			break;
+	}
+
+	return zspage;
+}
+
+static inline int __zs_cpu_up(struct mapping_area *area)
+{
+	/*
+	 * Make sure we don't leak memory if a cpu UP notification
+	 * and zs_init() race and both call zs_cpu_up() on the same cpu
+	 */
+	if (area->vm_buf)
+		return 0;
+	area->vm_buf = kmalloc(ZS_MAX_ALLOC_SIZE, GFP_KERNEL);
+	if (!area->vm_buf)
+		return -ENOMEM;
+	return 0;
+}
+
+static inline void __zs_cpu_down(struct mapping_area *area)
+{
+	kfree(area->vm_buf);
+	area->vm_buf = NULL;
+}
+
+static void *__zs_map_object(struct mapping_area *area,
+			struct page *pages[2], int off, int size)
+{
+	int sizes[2];
+	void *addr;
+	char *buf = area->vm_buf;
+
+	/* disable page faults to match kmap_atomic() return conditions */
+	pagefault_disable();
+
+	/* no read fastpath */
+	if (area->vm_mm == ZS_MM_WO)
+		goto out;
+
+	sizes[0] = PAGE_SIZE - off;
+	sizes[1] = size - sizes[0];
+
+	/* copy object to per-cpu buffer */
+	addr = kmap_atomic(pages[0]);
+	memcpy(buf, addr + off, sizes[0]);
+	kunmap_atomic(addr);
+	addr = kmap_atomic(pages[1]);
+	memcpy(buf + sizes[0], addr, sizes[1]);
+	kunmap_atomic(addr);
+out:
+	return area->vm_buf;
+}
+
+static void __zs_unmap_object(struct mapping_area *area,
+			struct page *pages[2], int off, int size)
+{
+	int sizes[2];
+	void *addr;
+	char *buf;
+
+	/* no write fastpath */
+	if (area->vm_mm == ZS_MM_RO)
+		goto out;
+
+	buf = area->vm_buf;
+	buf = buf + ZS_HANDLE_SIZE;
+	size -= ZS_HANDLE_SIZE;
+	off += ZS_HANDLE_SIZE;
+
+	sizes[0] = PAGE_SIZE - off;
+	sizes[1] = size - sizes[0];
+
+	/* copy per-cpu buffer to object */
+	addr = kmap_atomic(pages[0]);
+	memcpy(addr + off, buf, sizes[0]);
+	kunmap_atomic(addr);
+	addr = kmap_atomic(pages[1]);
+	memcpy(addr, buf + sizes[0], sizes[1]);
+	kunmap_atomic(addr);
+
+out:
+	/* enable page faults to match kunmap_atomic() return conditions */
+	pagefault_enable();
+}
+
+static int zs_cpu_prepare(unsigned int cpu)
+{
+	struct mapping_area *area;
+
+	area = &per_cpu(zs_map_area, cpu);
+	return __zs_cpu_up(area);
+}
+
+static int zs_cpu_dead(unsigned int cpu)
+{
+	struct mapping_area *area;
+
+	area = &per_cpu(zs_map_area, cpu);
+	__zs_cpu_down(area);
+	return 0;
+}
+
+static bool can_merge(struct size_class *prev, int pages_per_zspage,
+					int objs_per_zspage)
+{
+	if (prev->pages_per_zspage == pages_per_zspage &&
+		prev->objs_per_zspage == objs_per_zspage)
+		return true;
+
+	return false;
+}
+
+static bool zspage_full(struct size_class *class, struct zspage *zspage)
+{
+	return get_zspage_inuse(zspage) == class->objs_per_zspage;
+}
+
+unsigned long zs_get_total_pages(struct zs_pool *pool)
+{
+	return atomic_long_read(&pool->pages_allocated);
+}
+EXPORT_SYMBOL_GPL(zs_get_total_pages);
+
+/**
+ * zs_map_object - get address of allocated object from handle.
+ * @pool: pool from which the object was allocated
+ * @handle: handle returned from zs_malloc
+ * @mm: maping mode to use
+ *
+ * Before using an object allocated from zs_malloc, it must be mapped using
+ * this function. When done with the object, it must be unmapped using
+ * zs_unmap_object.
+ *
+ * Only one object can be mapped per cpu at a time. There is no protection
+ * against nested mappings.
+ *
+ * This function returns with preemption and page faults disabled.
+ */
+void *zs_map_object(struct zs_pool *pool, unsigned long handle,
+			enum zs_mapmode mm)
+{
+	struct zspage *zspage;
+	struct page *page;
+	unsigned long obj, off;
+	unsigned int obj_idx;
+
+	unsigned int class_idx;
+	enum fullness_group fg;
+	struct size_class *class;
+	struct mapping_area *area;
+	struct page *pages[2];
+	void *ret;
+
+	/*
+	 * Because we use per-cpu mapping areas shared among the
+	 * pools/users, we can't allow mapping in interrupt context
+	 * because it can corrupt another users mappings.
+	 */
+	BUG_ON(in_interrupt());
+
+	/* From now on, migration cannot move the object */
+	pin_tag(handle);
+
+	obj = handle_to_obj(handle);
+	obj_to_location(obj, &page, &obj_idx);
+	zspage = get_zspage(page);
+
+	/* migration cannot move any subpage in this zspage */
+	migrate_read_lock(zspage);
+
+	get_zspage_mapping(zspage, &class_idx, &fg);
+	class = pool->size_class[class_idx];
+	off = (class->size * obj_idx) & ~PAGE_MASK;
+
+	area = &get_cpu_var(zs_map_area);
+	area->vm_mm = mm;
+	if (off + class->size <= PAGE_SIZE) {
+		/* this object is contained entirely within a page */
+		area->vm_addr = kmap_atomic(page);
+		ret = area->vm_addr + off;
+		goto out;
+	}
+
+	/* this object spans two pages */
+	pages[0] = page;
+	pages[1] = get_next_page(page);
+	BUG_ON(!pages[1]);
+
+	ret = __zs_map_object(area, pages, off, class->size);
+out:
+	if (likely(!PageHugeObject(page)))
+		ret += ZS_HANDLE_SIZE;
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(zs_map_object);
+
+void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
+{
+	struct zspage *zspage;
+	struct page *page;
+	unsigned long obj, off;
+	unsigned int obj_idx;
+
+	unsigned int class_idx;
+	enum fullness_group fg;
+	struct size_class *class;
+	struct mapping_area *area;
+
+	obj = handle_to_obj(handle);
+	obj_to_location(obj, &page, &obj_idx);
+	zspage = get_zspage(page);
+	get_zspage_mapping(zspage, &class_idx, &fg);
+	class = pool->size_class[class_idx];
+	off = (class->size * obj_idx) & ~PAGE_MASK;
+
+	area = this_cpu_ptr(&zs_map_area);
+	if (off + class->size <= PAGE_SIZE)
+		kunmap_atomic(area->vm_addr);
+	else {
+		struct page *pages[2];
+
+		pages[0] = page;
+		pages[1] = get_next_page(page);
+		BUG_ON(!pages[1]);
+
+		__zs_unmap_object(area, pages, off, class->size);
+	}
+	put_cpu_var(zs_map_area);
+
+	migrate_read_unlock(zspage);
+	unpin_tag(handle);
+}
+EXPORT_SYMBOL_GPL(zs_unmap_object);
+
+/**
+ * zs_huge_class_size() - Returns the size (in bytes) of the first huge
+ *                        zsmalloc &size_class.
+ * @pool: zsmalloc pool to use
+ *
+ * The function returns the size of the first huge class - any object of equal
+ * or bigger size will be stored in zspage consisting of a single physical
+ * page.
+ *
+ * Context: Any context.
+ *
+ * Return: the size (in bytes) of the first huge zsmalloc &size_class.
+ */
+size_t zs_huge_class_size(struct zs_pool *pool)
+{
+	return huge_class_size;
+}
+EXPORT_SYMBOL_GPL(zs_huge_class_size);
+
+static unsigned long obj_malloc(struct size_class *class,
+				struct zspage *zspage, unsigned long handle)
+{
+	int i, nr_page, offset;
+	unsigned long obj;
+	struct link_free *link;
+
+	struct page *m_page;
+	unsigned long m_offset;
+	void *vaddr;
+
+	handle |= OBJ_ALLOCATED_TAG;
+	obj = get_freeobj(zspage);
+
+	offset = obj * class->size;
+	nr_page = offset >> PAGE_SHIFT;
+	m_offset = offset & ~PAGE_MASK;
+	m_page = get_first_page(zspage);
+
+	for (i = 0; i < nr_page; i++)
+		m_page = get_next_page(m_page);
+
+	vaddr = kmap_atomic(m_page);
+	link = (struct link_free *)vaddr + m_offset / sizeof(*link);
+	set_freeobj(zspage, link->next >> OBJ_TAG_BITS);
+	if (likely(!PageHugeObject(m_page)))
+		/* record handle in the header of allocated chunk */
+		link->handle = handle;
+	else
+		/* record handle to page->index */
+		zspage->first_page->index = handle;
+
+	kunmap_atomic(vaddr);
+	mod_zspage_inuse(zspage, 1);
+	zs_stat_inc(class, OBJ_USED, 1);
+
+	obj = location_to_obj(m_page, obj);
+
+	return obj;
+}
+
+
+/**
+ * zs_malloc - Allocate block of given size from pool.
+ * @pool: pool to allocate from
+ * @size: size of block to allocate
+ * @gfp: gfp flags when allocating object
+ *
+ * On success, handle to the allocated object is returned,
+ * otherwise 0.
+ * Allocation requests with size > ZS_MAX_ALLOC_SIZE will fail.
+ */
+unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t gfp)
+{
+	unsigned long handle, obj;
+	struct size_class *class;
+	enum fullness_group newfg;
+	struct zspage *zspage;
+
+	if (unlikely(!size || size > ZS_MAX_ALLOC_SIZE))
+		return 0;
+
+	handle = cache_alloc_handle(pool, gfp);
+	if (!handle)
+		return 0;
+
+	/* extra space in chunk to keep the handle */
+	size += ZS_HANDLE_SIZE;
+	class = pool->size_class[get_size_class_index(size)];
+
+	spin_lock(&class->lock);
+	zspage = find_get_zspage(class);
+	if (likely(zspage)) {
+		obj = obj_malloc(class, zspage, handle);
+		/* Now move the zspage to another fullness group, if required */
+		fix_fullness_group(class, zspage);
+		record_obj(handle, obj);
+		spin_unlock(&class->lock);
+
+		return handle;
+	}
+
+	spin_unlock(&class->lock);
+
+	zspage = alloc_zspage(pool, class, gfp);
+	if (!zspage) {
+		cache_free_handle(pool, handle);
+		return 0;
+	}
+
+	spin_lock(&class->lock);
+	obj = obj_malloc(class, zspage, handle);
+	newfg = get_fullness_group(class, zspage);
+	insert_zspage(class, zspage, newfg);
+	set_zspage_mapping(zspage, class->index, newfg);
+	record_obj(handle, obj);
+	atomic_long_add(class->pages_per_zspage,
+				&pool->pages_allocated);
+	zs_stat_inc(class, OBJ_ALLOCATED, class->objs_per_zspage);
+
+	/* We completely set up zspage so mark them as movable */
+	SetZsPageMovable(pool, zspage);
+	spin_unlock(&class->lock);
+
+	return handle;
+}
+EXPORT_SYMBOL_GPL(zs_malloc);
+
+static void obj_free(struct size_class *class, unsigned long obj)
+{
+	struct link_free *link;
+	struct zspage *zspage;
+	struct page *f_page;
+	unsigned long f_offset;
+	unsigned int f_objidx;
+	void *vaddr;
+
+	obj &= ~OBJ_ALLOCATED_TAG;
+	obj_to_location(obj, &f_page, &f_objidx);
+	f_offset = (class->size * f_objidx) & ~PAGE_MASK;
+	zspage = get_zspage(f_page);
+
+	vaddr = kmap_atomic(f_page);
+
+	/* Insert this object in containing zspage's freelist */
+	link = (struct link_free *)(vaddr + f_offset);
+	link->next = get_freeobj(zspage) << OBJ_TAG_BITS;
+	kunmap_atomic(vaddr);
+	set_freeobj(zspage, f_objidx);
+	mod_zspage_inuse(zspage, -1);
+	zs_stat_dec(class, OBJ_USED, 1);
+}
+
+void zs_free(struct zs_pool *pool, unsigned long handle)
+{
+	struct zspage *zspage;
+	struct page *f_page;
+	unsigned long obj;
+	unsigned int f_objidx;
+	int class_idx;
+	struct size_class *class;
+	enum fullness_group fullness;
+	bool isolated;
+
+	if (unlikely(!handle))
+		return;
+
+	pin_tag(handle);
+	obj = handle_to_obj(handle);
+	obj_to_location(obj, &f_page, &f_objidx);
+	zspage = get_zspage(f_page);
+
+	migrate_read_lock(zspage);
+
+	get_zspage_mapping(zspage, &class_idx, &fullness);
+	class = pool->size_class[class_idx];
+
+	spin_lock(&class->lock);
+	obj_free(class, obj);
+	fullness = fix_fullness_group(class, zspage);
+	if (fullness != ZS_EMPTY) {
+		migrate_read_unlock(zspage);
+		goto out;
+	}
+
+	isolated = is_zspage_isolated(zspage);
+	migrate_read_unlock(zspage);
+	/* If zspage is isolated, zs_page_putback will free the zspage */
+	if (likely(!isolated))
+		free_zspage(pool, class, zspage);
+out:
+
+	spin_unlock(&class->lock);
+	unpin_tag(handle);
+	cache_free_handle(pool, handle);
+}
+EXPORT_SYMBOL_GPL(zs_free);
+
+static void zs_object_copy(struct size_class *class, unsigned long dst,
+				unsigned long src)
+{
+	struct page *s_page, *d_page;
+	unsigned int s_objidx, d_objidx;
+	unsigned long s_off, d_off;
+	void *s_addr, *d_addr;
+	int s_size, d_size, size;
+	int written = 0;
+
+	s_size = d_size = class->size;
+
+	obj_to_location(src, &s_page, &s_objidx);
+	obj_to_location(dst, &d_page, &d_objidx);
+
+	s_off = (class->size * s_objidx) & ~PAGE_MASK;
+	d_off = (class->size * d_objidx) & ~PAGE_MASK;
+
+	if (s_off + class->size > PAGE_SIZE)
+		s_size = PAGE_SIZE - s_off;
+
+	if (d_off + class->size > PAGE_SIZE)
+		d_size = PAGE_SIZE - d_off;
+
+	s_addr = kmap_atomic(s_page);
+	d_addr = kmap_atomic(d_page);
+
+	while (1) {
+		size = min(s_size, d_size);
+		memcpy(d_addr + d_off, s_addr + s_off, size);
+		written += size;
+
+		if (written == class->size)
+			break;
+
+		s_off += size;
+		s_size -= size;
+		d_off += size;
+		d_size -= size;
+
+		if (s_off >= PAGE_SIZE) {
+			kunmap_atomic(d_addr);
+			kunmap_atomic(s_addr);
+			s_page = get_next_page(s_page);
+			s_addr = kmap_atomic(s_page);
+			d_addr = kmap_atomic(d_page);
+			s_size = class->size - written;
+			s_off = 0;
+		}
+
+		if (d_off >= PAGE_SIZE) {
+			kunmap_atomic(d_addr);
+			d_page = get_next_page(d_page);
+			d_addr = kmap_atomic(d_page);
+			d_size = class->size - written;
+			d_off = 0;
+		}
+	}
+
+	kunmap_atomic(d_addr);
+	kunmap_atomic(s_addr);
+}
+
+/*
+ * Find alloced object in zspage from index object and
+ * return handle.
+ */
+static unsigned long find_alloced_obj(struct size_class *class,
+					struct page *page, int *obj_idx)
+{
+	unsigned long head;
+	int offset = 0;
+	int index = *obj_idx;
+	unsigned long handle = 0;
+	void *addr = kmap_atomic(page);
+
+	offset = get_first_obj_offset(page);
+	offset += class->size * index;
+
+	while (offset < PAGE_SIZE) {
+		head = obj_to_head(page, addr + offset);
+		if (head & OBJ_ALLOCATED_TAG) {
+			handle = head & ~OBJ_ALLOCATED_TAG;
+			if (trypin_tag(handle))
+				break;
+			handle = 0;
+		}
+
+		offset += class->size;
+		index++;
+	}
+
+	kunmap_atomic(addr);
+
+	*obj_idx = index;
+
+	return handle;
+}
+
+struct zs_compact_control {
+	/* Source spage for migration which could be a subpage of zspage */
+	struct page *s_page;
+	/* Destination page for migration which should be a first page
+	 * of zspage. */
+	struct page *d_page;
+	 /* Starting object index within @s_page which used for live object
+	  * in the subpage. */
+	int obj_idx;
+};
+
+static int migrate_zspage(struct zs_pool *pool, struct size_class *class,
+				struct zs_compact_control *cc)
+{
+	unsigned long used_obj, free_obj;
+	unsigned long handle;
+	struct page *s_page = cc->s_page;
+	struct page *d_page = cc->d_page;
+	int obj_idx = cc->obj_idx;
+	int ret = 0;
+
+	while (1) {
+		handle = find_alloced_obj(class, s_page, &obj_idx);
+		if (!handle) {
+			s_page = get_next_page(s_page);
+			if (!s_page)
+				break;
+			obj_idx = 0;
+			continue;
+		}
+
+		/* Stop if there is no more space */
+		if (zspage_full(class, get_zspage(d_page))) {
+			unpin_tag(handle);
+			ret = -ENOMEM;
+			break;
+		}
+
+		used_obj = handle_to_obj(handle);
+		free_obj = obj_malloc(class, get_zspage(d_page), handle);
+		zs_object_copy(class, free_obj, used_obj);
+		obj_idx++;
+		/*
+		 * record_obj updates handle's value to free_obj and it will
+		 * invalidate lock bit(ie, HANDLE_PIN_BIT) of handle, which
+		 * breaks synchronization using pin_tag(e,g, zs_free) so
+		 * let's keep the lock bit.
+		 */
+		free_obj |= BIT(HANDLE_PIN_BIT);
+		record_obj(handle, free_obj);
+		unpin_tag(handle);
+		obj_free(class, used_obj);
+	}
+
+	/* Remember last position in this iteration */
+	cc->s_page = s_page;
+	cc->obj_idx = obj_idx;
+
+	return ret;
+}
+
+static struct zspage *isolate_zspage(struct size_class *class, bool source)
+{
+	int i;
+	struct zspage *zspage;
+	enum fullness_group fg[2] = {ZS_ALMOST_EMPTY, ZS_ALMOST_FULL};
+
+	if (!source) {
+		fg[0] = ZS_ALMOST_FULL;
+		fg[1] = ZS_ALMOST_EMPTY;
+	}
+
+	for (i = 0; i < 2; i++) {
+		zspage = list_first_entry_or_null(&class->fullness_list[fg[i]],
+							struct zspage, list);
+		if (zspage) {
+			VM_BUG_ON(is_zspage_isolated(zspage));
+			remove_zspage(class, zspage, fg[i]);
+			return zspage;
+		}
+	}
+
+	return zspage;
+}
+
+/*
+ * putback_zspage - add @zspage into right class's fullness list
+ * @class: destination class
+ * @zspage: target page
+ *
+ * Return @zspage's fullness_group
+ */
+static enum fullness_group putback_zspage(struct size_class *class,
+			struct zspage *zspage)
+{
+	enum fullness_group fullness;
+
+	VM_BUG_ON(is_zspage_isolated(zspage));
+
+	fullness = get_fullness_group(class, zspage);
+	insert_zspage(class, zspage, fullness);
+	set_zspage_mapping(zspage, class->index, fullness);
+
+	return fullness;
+}
+
+#ifdef CONFIG_COMPACTION
+/*
+ * To prevent zspage destroy during migration, zspage freeing should
+ * hold locks of all pages in the zspage.
+ */
+static void lock_zspage(struct zspage *zspage)
+{
+	struct page *curr_page, *page;
+
+	/*
+	 * Pages we haven't locked yet can be migrated off the list while we're
+	 * trying to lock them, so we need to be careful and only attempt to
+	 * lock each page under migrate_read_lock(). Otherwise, the page we lock
+	 * may no longer belong to the zspage. This means that we may wait for
+	 * the wrong page to unlock, so we must take a reference to the page
+	 * prior to waiting for it to unlock outside migrate_read_lock().
+	 */
+	while (1) {
+		migrate_read_lock(zspage);
+		page = get_first_page(zspage);
+		if (trylock_page(page))
+			break;
+		get_page(page);
+		migrate_read_unlock(zspage);
+		wait_on_page_locked(page);
+		put_page(page);
+	}
+
+	curr_page = page;
+	while ((page = get_next_page(curr_page))) {
+		if (trylock_page(page)) {
+			curr_page = page;
+		} else {
+			get_page(page);
+			migrate_read_unlock(zspage);
+			wait_on_page_locked(page);
+			put_page(page);
+			migrate_read_lock(zspage);
+		}
+	}
+	migrate_read_unlock(zspage);
+}
+
+static int zs_init_fs_context(struct fs_context *fc)
+{
+	return init_pseudo(fc, ZSMALLOC_MAGIC) ? 0 : -ENOMEM;
+}
+
+static struct file_system_type zsmalloc_fs = {
+	.name		= "zsmalloc",
+	.init_fs_context = zs_init_fs_context,
+	.kill_sb	= kill_anon_super,
+};
+
+static int zsmalloc_mount(void)
+{
+	int ret = 0;
+
+	zsmalloc_mnt = kern_mount(&zsmalloc_fs);
+	if (IS_ERR(zsmalloc_mnt))
+		ret = PTR_ERR(zsmalloc_mnt);
+
+	return ret;
+}
+
+static void zsmalloc_unmount(void)
+{
+	kern_unmount(zsmalloc_mnt);
+}
+
+static void migrate_lock_init(struct zspage *zspage)
+{
+	rwlock_init(&zspage->lock);
+}
+
+static void migrate_read_lock(struct zspage *zspage) __acquires(&zspage->lock)
+{
+	read_lock(&zspage->lock);
+}
+
+static void migrate_read_unlock(struct zspage *zspage) __releases(&zspage->lock)
+{
+	read_unlock(&zspage->lock);
+}
+
+static void migrate_write_lock(struct zspage *zspage)
+{
+	write_lock(&zspage->lock);
+}
+
+static void migrate_write_unlock(struct zspage *zspage)
+{
+	write_unlock(&zspage->lock);
+}
+
+/* Number of isolated subpage for *page migration* in this zspage */
+static void inc_zspage_isolation(struct zspage *zspage)
+{
+	zspage->isolated++;
+}
+
+static void dec_zspage_isolation(struct zspage *zspage)
+{
+	zspage->isolated--;
+}
+
+static void putback_zspage_deferred(struct zs_pool *pool,
+				    struct size_class *class,
+				    struct zspage *zspage)
+{
+	enum fullness_group fg;
+
+	fg = putback_zspage(class, zspage);
+	if (fg == ZS_EMPTY)
+		schedule_work(&pool->free_work);
+
+}
+
+static inline void zs_pool_dec_isolated(struct zs_pool *pool)
+{
+	VM_BUG_ON(atomic_long_read(&pool->isolated_pages) <= 0);
+	atomic_long_dec(&pool->isolated_pages);
+	/*
+	 * Checking pool->destroying must happen after atomic_long_dec()
+	 * for pool->isolated_pages above. Paired with the smp_mb() in
+	 * zs_unregister_migration().
+	 */
+	smp_mb__after_atomic();
+	if (atomic_long_read(&pool->isolated_pages) == 0 && pool->destroying)
+		wake_up_all(&pool->migration_wait);
+}
+
+static void replace_sub_page(struct size_class *class, struct zspage *zspage,
+				struct page *newpage, struct page *oldpage)
+{
+	struct page *page;
+	struct page *pages[ZS_MAX_PAGES_PER_ZSPAGE] = {NULL, };
+	int idx = 0;
+
+	page = get_first_page(zspage);
+	do {
+		if (page == oldpage)
+			pages[idx] = newpage;
+		else
+			pages[idx] = page;
+		idx++;
+	} while ((page = get_next_page(page)) != NULL);
+
+	create_page_chain(class, zspage, pages);
+	set_first_obj_offset(newpage, get_first_obj_offset(oldpage));
+	if (unlikely(PageHugeObject(oldpage)))
+		newpage->index = oldpage->index;
+	__SetPageMovable(newpage, page_mapping(oldpage));
+}
+
+static bool zs_page_isolate(struct page *page, isolate_mode_t mode)
+{
+	struct zs_pool *pool;
+	struct size_class *class;
+	int class_idx;
+	enum fullness_group fullness;
+	struct zspage *zspage;
+	struct address_space *mapping;
+
+	/*
+	 * Page is locked so zspage couldn't be destroyed. For detail, look at
+	 * lock_zspage in free_zspage.
+	 */
+	VM_BUG_ON_PAGE(!PageMovable(page), page);
+	VM_BUG_ON_PAGE(PageIsolated(page), page);
+
+	zspage = get_zspage(page);
+
+	/*
+	 * Without class lock, fullness could be stale while class_idx is okay
+	 * because class_idx is constant unless page is freed so we should get
+	 * fullness again under class lock.
+	 */
+	get_zspage_mapping(zspage, &class_idx, &fullness);
+	mapping = page_mapping(page);
+	pool = mapping->private_data;
+	class = pool->size_class[class_idx];
+
+	spin_lock(&class->lock);
+	if (get_zspage_inuse(zspage) == 0) {
+		spin_unlock(&class->lock);
+		return false;
+	}
+
+	/* zspage is isolated for object migration */
+	if (list_empty(&zspage->list) && !is_zspage_isolated(zspage)) {
+		spin_unlock(&class->lock);
+		return false;
+	}
+
+	/*
+	 * If this is first time isolation for the zspage, isolate zspage from
+	 * size_class to prevent further object allocation from the zspage.
+	 */
+	if (!list_empty(&zspage->list) && !is_zspage_isolated(zspage)) {
+		get_zspage_mapping(zspage, &class_idx, &fullness);
+		atomic_long_inc(&pool->isolated_pages);
+		remove_zspage(class, zspage, fullness);
+	}
+
+	inc_zspage_isolation(zspage);
+	spin_unlock(&class->lock);
+
+	return true;
+}
+
+static int zs_page_migrate(struct address_space *mapping, struct page *newpage,
+		struct page *page, enum migrate_mode mode)
+{
+	struct zs_pool *pool;
+	struct size_class *class;
+	int class_idx;
+	enum fullness_group fullness;
+	struct zspage *zspage;
+	struct page *dummy;
+	void *s_addr, *d_addr, *addr;
+	int offset, pos;
+	unsigned long handle, head;
+	unsigned long old_obj, new_obj;
+	unsigned int obj_idx;
+	int ret = -EAGAIN;
+
+	/*
+	 * We cannot support the _NO_COPY case here, because copy needs to
+	 * happen under the zs lock, which does not work with
+	 * MIGRATE_SYNC_NO_COPY workflow.
+	 */
+	if (mode == MIGRATE_SYNC_NO_COPY)
+		return -EINVAL;
+
+	VM_BUG_ON_PAGE(!PageMovable(page), page);
+	VM_BUG_ON_PAGE(!PageIsolated(page), page);
+
+	zspage = get_zspage(page);
+
+	/* Concurrent compactor cannot migrate any subpage in zspage */
+	migrate_write_lock(zspage);
+	get_zspage_mapping(zspage, &class_idx, &fullness);
+	pool = mapping->private_data;
+	class = pool->size_class[class_idx];
+	offset = get_first_obj_offset(page);
+
+	spin_lock(&class->lock);
+	if (!get_zspage_inuse(zspage)) {
+		/*
+		 * Set "offset" to end of the page so that every loops
+		 * skips unnecessary object scanning.
+		 */
+		offset = PAGE_SIZE;
+	}
+
+	pos = offset;
+	s_addr = kmap_atomic(page);
+	while (pos < PAGE_SIZE) {
+		head = obj_to_head(page, s_addr + pos);
+		if (head & OBJ_ALLOCATED_TAG) {
+			handle = head & ~OBJ_ALLOCATED_TAG;
+			if (!trypin_tag(handle))
+				goto unpin_objects;
+		}
+		pos += class->size;
+	}
+
+	/*
+	 * Here, any user cannot access all objects in the zspage so let's move.
+	 */
+	d_addr = kmap_atomic(newpage);
+	memcpy(d_addr, s_addr, PAGE_SIZE);
+	kunmap_atomic(d_addr);
+
+	for (addr = s_addr + offset; addr < s_addr + pos;
+					addr += class->size) {
+		head = obj_to_head(page, addr);
+		if (head & OBJ_ALLOCATED_TAG) {
+			handle = head & ~OBJ_ALLOCATED_TAG;
+			if (!testpin_tag(handle))
+				BUG();
+
+			old_obj = handle_to_obj(handle);
+			obj_to_location(old_obj, &dummy, &obj_idx);
+			new_obj = (unsigned long)location_to_obj(newpage,
+								obj_idx);
+			new_obj |= BIT(HANDLE_PIN_BIT);
+			record_obj(handle, new_obj);
+		}
+	}
+
+	replace_sub_page(class, zspage, newpage, page);
+	get_page(newpage);
+
+	dec_zspage_isolation(zspage);
+
+	/*
+	 * Page migration is done so let's putback isolated zspage to
+	 * the list if @page is final isolated subpage in the zspage.
+	 */
+	if (!is_zspage_isolated(zspage)) {
+		/*
+		 * We cannot race with zs_destroy_pool() here because we wait
+		 * for isolation to hit zero before we start destroying.
+		 * Also, we ensure that everyone can see pool->destroying before
+		 * we start waiting.
+		 */
+		putback_zspage_deferred(pool, class, zspage);
+		zs_pool_dec_isolated(pool);
+	}
+
+	if (page_zone(newpage) != page_zone(page)) {
+		dec_zone_page_state(page, NR_ZSPAGES);
+		inc_zone_page_state(newpage, NR_ZSPAGES);
+	}
+
+	reset_page(page);
+	put_page(page);
+	page = newpage;
+
+	ret = MIGRATEPAGE_SUCCESS;
+unpin_objects:
+	for (addr = s_addr + offset; addr < s_addr + pos;
+						addr += class->size) {
+		head = obj_to_head(page, addr);
+		if (head & OBJ_ALLOCATED_TAG) {
+			handle = head & ~OBJ_ALLOCATED_TAG;
+			if (!testpin_tag(handle))
+				BUG();
+			unpin_tag(handle);
+		}
+	}
+	kunmap_atomic(s_addr);
+	spin_unlock(&class->lock);
+	migrate_write_unlock(zspage);
+
+	return ret;
+}
+
+static void zs_page_putback(struct page *page)
+{
+	struct zs_pool *pool;
+	struct size_class *class;
+	int class_idx;
+	enum fullness_group fg;
+	struct address_space *mapping;
+	struct zspage *zspage;
+
+	VM_BUG_ON_PAGE(!PageMovable(page), page);
+	VM_BUG_ON_PAGE(!PageIsolated(page), page);
+
+	zspage = get_zspage(page);
+	get_zspage_mapping(zspage, &class_idx, &fg);
+	mapping = page_mapping(page);
+	pool = mapping->private_data;
+	class = pool->size_class[class_idx];
+
+	spin_lock(&class->lock);
+	dec_zspage_isolation(zspage);
+	if (!is_zspage_isolated(zspage)) {
+		/*
+		 * Due to page_lock, we cannot free zspage immediately
+		 * so let's defer.
+		 */
+		putback_zspage_deferred(pool, class, zspage);
+		zs_pool_dec_isolated(pool);
+	}
+	spin_unlock(&class->lock);
+}
+
+static const struct address_space_operations zsmalloc_aops = {
+	.isolate_page = zs_page_isolate,
+	.migratepage = zs_page_migrate,
+	.putback_page = zs_page_putback,
+};
+
+static int zs_register_migration(struct zs_pool *pool)
+{
+	pool->inode = alloc_anon_inode(zsmalloc_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 = &zsmalloc_aops;
+	return 0;
+}
+
+static bool pool_isolated_are_drained(struct zs_pool *pool)
+{
+	return atomic_long_read(&pool->isolated_pages) == 0;
+}
+
+/* Function for resolving migration */
+static void wait_for_isolated_drain(struct zs_pool *pool)
+{
+
+	/*
+	 * We're in the process of destroying the pool, so there are no
+	 * active allocations. zs_page_isolate() fails for completely free
+	 * zspages, so we need only wait for the zs_pool's isolated
+	 * count to hit zero.
+	 */
+	wait_event(pool->migration_wait,
+		   pool_isolated_are_drained(pool));
+}
+
+static void zs_unregister_migration(struct zs_pool *pool)
+{
+	pool->destroying = true;
+	/*
+	 * We need a memory barrier here to ensure global visibility of
+	 * pool->destroying. Thus pool->isolated pages will either be 0 in which
+	 * case we don't care, or it will be > 0 and pool->destroying will
+	 * ensure that we wake up once isolation hits 0.
+	 */
+	smp_mb();
+	wait_for_isolated_drain(pool); /* This can block */
+	flush_work(&pool->free_work);
+	iput(pool->inode);
+}
+
+/*
+ * Caller should hold page_lock of all pages in the zspage
+ * In here, we cannot use zspage meta data.
+ */
+static void async_free_zspage(struct work_struct *work)
+{
+	int i;
+	struct size_class *class;
+	unsigned int class_idx;
+	enum fullness_group fullness;
+	struct zspage *zspage, *tmp;
+	LIST_HEAD(free_pages);
+	struct zs_pool *pool = container_of(work, struct zs_pool,
+					free_work);
+
+	for (i = 0; i < ZS_SIZE_CLASSES; i++) {
+		class = pool->size_class[i];
+		if (class->index != i)
+			continue;
+
+		spin_lock(&class->lock);
+		list_splice_init(&class->fullness_list[ZS_EMPTY], &free_pages);
+		spin_unlock(&class->lock);
+	}
+
+
+	list_for_each_entry_safe(zspage, tmp, &free_pages, list) {
+		list_del(&zspage->list);
+		lock_zspage(zspage);
+
+		get_zspage_mapping(zspage, &class_idx, &fullness);
+		VM_BUG_ON(fullness != ZS_EMPTY);
+		class = pool->size_class[class_idx];
+		spin_lock(&class->lock);
+		__free_zspage(pool, pool->size_class[class_idx], zspage);
+		spin_unlock(&class->lock);
+	}
+};
+
+static void kick_deferred_free(struct zs_pool *pool)
+{
+	schedule_work(&pool->free_work);
+}
+
+static void init_deferred_free(struct zs_pool *pool)
+{
+	INIT_WORK(&pool->free_work, async_free_zspage);
+}
+
+static void SetZsPageMovable(struct zs_pool *pool, struct zspage *zspage)
+{
+	struct page *page = get_first_page(zspage);
+
+	do {
+		WARN_ON(!trylock_page(page));
+		__SetPageMovable(page, pool->inode->i_mapping);
+		unlock_page(page);
+	} while ((page = get_next_page(page)) != NULL);
+}
+#endif
+
+/*
+ *
+ * Based on the number of unused allocated objects calculate
+ * and return the number of pages that we can free.
+ */
+static unsigned long zs_can_compact(struct size_class *class)
+{
+	unsigned long obj_wasted;
+	unsigned long obj_allocated = zs_stat_get(class, OBJ_ALLOCATED);
+	unsigned long obj_used = zs_stat_get(class, OBJ_USED);
+
+	if (obj_allocated <= obj_used)
+		return 0;
+
+	obj_wasted = obj_allocated - obj_used;
+	obj_wasted /= class->objs_per_zspage;
+
+	return obj_wasted * class->pages_per_zspage;
+}
+
+static unsigned long __zs_compact(struct zs_pool *pool,
+				  struct size_class *class)
+{
+	struct zs_compact_control cc;
+	struct zspage *src_zspage;
+	struct zspage *dst_zspage = NULL;
+	unsigned long pages_freed = 0;
+
+	spin_lock(&class->lock);
+	while ((src_zspage = isolate_zspage(class, true))) {
+
+		if (!zs_can_compact(class))
+			break;
+
+		cc.obj_idx = 0;
+		cc.s_page = get_first_page(src_zspage);
+
+		while ((dst_zspage = isolate_zspage(class, false))) {
+			cc.d_page = get_first_page(dst_zspage);
+			/*
+			 * If there is no more space in dst_page, resched
+			 * and see if anyone had allocated another zspage.
+			 */
+			if (!migrate_zspage(pool, class, &cc))
+				break;
+
+			putback_zspage(class, dst_zspage);
+		}
+
+		/* Stop if we couldn't find slot */
+		if (dst_zspage == NULL)
+			break;
+
+		putback_zspage(class, dst_zspage);
+		if (putback_zspage(class, src_zspage) == ZS_EMPTY) {
+			free_zspage(pool, class, src_zspage);
+			pages_freed += class->pages_per_zspage;
+		}
+		spin_unlock(&class->lock);
+		cond_resched();
+		spin_lock(&class->lock);
+	}
+
+	if (src_zspage)
+		putback_zspage(class, src_zspage);
+
+	spin_unlock(&class->lock);
+
+	return pages_freed;
+}
+
+unsigned long zs_compact(struct zs_pool *pool)
+{
+	int i;
+	struct size_class *class;
+	unsigned long pages_freed = 0;
+
+	for (i = ZS_SIZE_CLASSES - 1; i >= 0; i--) {
+		class = pool->size_class[i];
+		if (!class)
+			continue;
+		if (class->index != i)
+			continue;
+		pages_freed += __zs_compact(pool, class);
+	}
+	atomic_long_add(pages_freed, &pool->stats.pages_compacted);
+
+	return pages_freed;
+}
+EXPORT_SYMBOL_GPL(zs_compact);
+
+void zs_pool_stats(struct zs_pool *pool, struct zs_pool_stats *stats)
+{
+	memcpy(stats, &pool->stats, sizeof(struct zs_pool_stats));
+}
+EXPORT_SYMBOL_GPL(zs_pool_stats);
+
+static unsigned long zs_shrinker_scan(struct shrinker *shrinker,
+		struct shrink_control *sc)
+{
+	unsigned long pages_freed;
+	struct zs_pool *pool = container_of(shrinker, struct zs_pool,
+			shrinker);
+
+	/*
+	 * Compact classes and calculate compaction delta.
+	 * Can run concurrently with a manually triggered
+	 * (by user) compaction.
+	 */
+	pages_freed = zs_compact(pool);
+
+	return pages_freed ? pages_freed : SHRINK_STOP;
+}
+
+static unsigned long zs_shrinker_count(struct shrinker *shrinker,
+		struct shrink_control *sc)
+{
+	int i;
+	struct size_class *class;
+	unsigned long pages_to_free = 0;
+	struct zs_pool *pool = container_of(shrinker, struct zs_pool,
+			shrinker);
+
+	for (i = ZS_SIZE_CLASSES - 1; i >= 0; i--) {
+		class = pool->size_class[i];
+		if (!class)
+			continue;
+		if (class->index != i)
+			continue;
+
+		pages_to_free += zs_can_compact(class);
+	}
+
+	return pages_to_free;
+}
+
+static void zs_unregister_shrinker(struct zs_pool *pool)
+{
+	unregister_shrinker(&pool->shrinker);
+}
+
+static int zs_register_shrinker(struct zs_pool *pool)
+{
+	pool->shrinker.scan_objects = zs_shrinker_scan;
+	pool->shrinker.count_objects = zs_shrinker_count;
+	pool->shrinker.batch = 0;
+	pool->shrinker.seeks = DEFAULT_SEEKS;
+
+	return register_shrinker(&pool->shrinker);
+}
+
+/**
+ * zs_create_pool - Creates an allocation pool to work from.
+ * @name: pool name to be created
+ *
+ * This function must be called before anything when using
+ * the zsmalloc allocator.
+ *
+ * On success, a pointer to the newly created pool is returned,
+ * otherwise NULL.
+ */
+struct zs_pool *zs_create_pool(const char *name)
+{
+	int i;
+	struct zs_pool *pool;
+	struct size_class *prev_class = NULL;
+
+	pool = kzalloc(sizeof(*pool), GFP_KERNEL);
+	if (!pool)
+		return NULL;
+
+	init_deferred_free(pool);
+
+	pool->name = kstrdup(name, GFP_KERNEL);
+	if (!pool->name)
+		goto err;
+
+#ifdef CONFIG_COMPACTION
+	init_waitqueue_head(&pool->migration_wait);
+#endif
+
+	if (create_cache(pool))
+		goto err;
+
+	/*
+	 * Iterate reversely, because, size of size_class that we want to use
+	 * for merging should be larger or equal to current size.
+	 */
+	for (i = ZS_SIZE_CLASSES - 1; i >= 0; i--) {
+		int size;
+		int pages_per_zspage;
+		int objs_per_zspage;
+		struct size_class *class;
+		int fullness = 0;
+
+		size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA;
+		if (size > ZS_MAX_ALLOC_SIZE)
+			size = ZS_MAX_ALLOC_SIZE;
+		pages_per_zspage = get_pages_per_zspage(size);
+		objs_per_zspage = pages_per_zspage * PAGE_SIZE / size;
+
+		/*
+		 * We iterate from biggest down to smallest classes,
+		 * so huge_class_size holds the size of the first huge
+		 * class. Any object bigger than or equal to that will
+		 * endup in the huge class.
+		 */
+		if (pages_per_zspage != 1 && objs_per_zspage != 1 &&
+				!huge_class_size) {
+			huge_class_size = size;
+			/*
+			 * The object uses ZS_HANDLE_SIZE bytes to store the
+			 * handle. We need to subtract it, because zs_malloc()
+			 * unconditionally adds handle size before it performs
+			 * size class search - so object may be smaller than
+			 * huge class size, yet it still can end up in the huge
+			 * class because it grows by ZS_HANDLE_SIZE extra bytes
+			 * right before class lookup.
+			 */
+			huge_class_size -= (ZS_HANDLE_SIZE - 1);
+		}
+
+		/*
+		 * size_class is used for normal zsmalloc operation such
+		 * as alloc/free for that size. Although it is natural that we
+		 * have one size_class for each size, there is a chance that we
+		 * can get more memory utilization if we use one size_class for
+		 * many different sizes whose size_class have same
+		 * characteristics. So, we makes size_class point to
+		 * previous size_class if possible.
+		 */
+		if (prev_class) {
+			if (can_merge(prev_class, pages_per_zspage, objs_per_zspage)) {
+				pool->size_class[i] = prev_class;
+				continue;
+			}
+		}
+
+		class = kzalloc(sizeof(struct size_class), GFP_KERNEL);
+		if (!class)
+			goto err;
+
+		class->size = size;
+		class->index = i;
+		class->pages_per_zspage = pages_per_zspage;
+		class->objs_per_zspage = objs_per_zspage;
+		spin_lock_init(&class->lock);
+		pool->size_class[i] = class;
+		for (fullness = ZS_EMPTY; fullness < NR_ZS_FULLNESS;
+							fullness++)
+			INIT_LIST_HEAD(&class->fullness_list[fullness]);
+
+		prev_class = class;
+	}
+
+	/* debug only, don't abort if it fails */
+	zs_pool_stat_create(pool, name);
+
+	if (zs_register_migration(pool))
+		goto err;
+
+	/*
+	 * Not critical since shrinker is only used to trigger internal
+	 * defragmentation of the pool which is pretty optional thing.  If
+	 * registration fails we still can use the pool normally and user can
+	 * trigger compaction manually. Thus, ignore return code.
+	 */
+	zs_register_shrinker(pool);
+
+	return pool;
+
+err:
+	zs_destroy_pool(pool);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(zs_create_pool);
+
+void zs_destroy_pool(struct zs_pool *pool)
+{
+	int i;
+
+	zs_unregister_shrinker(pool);
+	zs_unregister_migration(pool);
+	zs_pool_stat_destroy(pool);
+
+	for (i = 0; i < ZS_SIZE_CLASSES; i++) {
+		int fg;
+		struct size_class *class = pool->size_class[i];
+
+		if (!class)
+			continue;
+
+		if (class->index != i)
+			continue;
+
+		for (fg = ZS_EMPTY; fg < NR_ZS_FULLNESS; fg++) {
+			if (!list_empty(&class->fullness_list[fg])) {
+				pr_info("Freeing non-empty class with size %db, fullness group %d\n",
+					class->size, fg);
+			}
+		}
+		kfree(class);
+	}
+
+	destroy_cache(pool);
+	kfree(pool->name);
+	kfree(pool);
+}
+EXPORT_SYMBOL_GPL(zs_destroy_pool);
+
+static int __init zs_init(void)
+{
+	int ret;
+
+	ret = zsmalloc_mount();
+	if (ret)
+		goto out;
+
+	ret = cpuhp_setup_state(CPUHP_MM_ZS_PREPARE, "mm/zsmalloc:prepare",
+				zs_cpu_prepare, zs_cpu_dead);
+	if (ret)
+		goto hp_setup_fail;
+
+#ifdef CONFIG_ZPOOL
+	zpool_register_driver(&zs_zpool_driver);
+#endif
+
+	zs_stat_init();
+
+	return 0;
+
+hp_setup_fail:
+	zsmalloc_unmount();
+out:
+	return ret;
+}
+
+static void __exit zs_exit(void)
+{
+#ifdef CONFIG_ZPOOL
+	zpool_unregister_driver(&zs_zpool_driver);
+#endif
+	zsmalloc_unmount();
+	cpuhp_remove_state(CPUHP_MM_ZS_PREPARE);
+
+	zs_stat_exit();
+}
+
+module_init(zs_init);
+module_exit(zs_exit);
+
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_AUTHOR("Nitin Gupta <ngupta@vflare.org>");