text: /*
   * 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 <asm/tlbflush.h>
  #include <asm/pgtable.h>
  #include <linux/cpumask.h>
  #include <linux/cpu.h>
  #include <linux/vmalloc.h>
  #include <linux/preempt.h>
  #include <linux/spinlock.h>
  #include <linux/types.h>
  #include <linux/debugfs.h>
  #include <linux/zsmalloc.h>
  #include <linux/zpool.h>
  #include <linux/mount.h>
  #include <linux/migrate.h>
  #include <linux/pagemap.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
   * as 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_PHYSMEM_BITS
  #ifdef CONFIG_HIGHMEM64G
  #define MAX_PHYSMEM_BITS 36
  #else /* !CONFIG_HIGHMEM64G */
  /*
   * If this definition of MAX_PHYSMEM_BITS is used, OBJ_INDEX_BITS will just
   * be PAGE_SHIFT
   */
  #define MAX_PHYSMEM_BITS BITS_PER_LONG
  #endif
  #endif
  #define _PFN_BITS		(MAX_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 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)
  
  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
  
  /*
   * number of size_classes
   */
  static int zs_size_classes;
  
  /*
   * 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;
  
  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;
  	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;
  	/*
  	 * To signify that register_shrinker() was successful
  	 * and unregister_shrinker() will not Oops.
  	 */
  	bool shrinker_enabled;
  #ifdef CONFIG_ZSMALLOC_STAT
  	struct dentry *stat_dentry;
  #endif
  #ifdef CONFIG_COMPACTION
  	struct inode *inode;
  	struct work_struct free_work;
  #endif
  };
  
  #define FULLNESS_BITS	2
  #define CLASS_BITS	8
  #define ISOLATED_BITS	3
  #define MAGIC_VAL_BITS	8
  
  struct zspage {
  	struct {
  		unsigned int fullness:FULLNESS_BITS;
  		unsigned int class:CLASS_BITS;
  		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 {
  #ifdef CONFIG_PGTABLE_MAPPING
  	struct vm_struct *vm; /* vm area for mapping object that span pages */
  #else
  	char *vm_buf; /* copy buffer for objects that span pages */
  #endif
  	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 int zs_zpool_shrink(void *pool, unsigned int pages,
  			unsigned int *reclaimed)
  {
  	return -EINVAL;
  }
  
  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: /* fallthru */
  	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 =	zs_zpool_malloc,
  	.free =		zs_zpool_free,
  	.shrink =	zs_zpool_shrink,
  	.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 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 set_zspage_inuse(struct zspage *zspage, int val)
  {
  	zspage->inuse = val;
  }
  
  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(zs_size_classes - 1, idx);
  }
  
  static inline void zs_stat_inc(struct size_class *class,
  				enum zs_stat_type type, unsigned long cnt)
  {
  	class->stats.objs[type] += cnt;
  }
  
  static inline void zs_stat_dec(struct size_class *class,
  				enum zs_stat_type type, unsigned long cnt)
  {
  	class->stats.objs[type] -= cnt;
  }
  
  static inline unsigned long zs_stat_get(struct size_class *class,
  				enum zs_stat_type 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);
  	if (!zs_stat_root)
  		pr_warn("debugfs 'zsmalloc' stat dir creation failed\n");
  }
  
  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;
  }
  
  static int zs_stats_size_open(struct inode *inode, struct file *file)
  {
  	return single_open(file, zs_stats_size_show, inode->i_private);
  }
  
  static const struct file_operations zs_stat_size_ops = {
  	.open           = zs_stats_size_open,
  	.read           = seq_read,
  	.llseek         = seq_lseek,
  	.release        = single_release,
  };
  
  static void zs_pool_stat_create(struct zs_pool *pool, const char *name)
  {
  	struct dentry *entry;
  
  	if (!zs_stat_root) {
  		pr_warn("no root stat dir, not creating <%s> stat dir\n", name);
  		return;
  	}
  
  	entry = debugfs_create_dir(name, zs_stat_root);
  	if (!entry) {
  		pr_warn("debugfs dir <%s> creation failed\n", name);
  		return;
  	}
  	pool->stat_dentry = entry;
  
  	entry = debugfs_create_file("classes", S_IFREG | S_IRUGO,
  			pool->stat_dentry, pool, &zs_stat_size_ops);
  	if (!entry) {
  		pr_warn("%s: debugfs file entry <%s> creation failed\n",
  				name, "classes");
  		debugfs_remove_recursive(pool->stat_dentry);
  		pool->stat_dentry = NULL;
  	}
  }
  
  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
   * @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)
  {
  	bit_spin_lock(HANDLE_PIN_BIT, (unsigned long *)handle);
  }
  
  static void unpin_tag(unsigned long handle)
  {
  	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;
  }
  
  /*
   * To prevent zspage destroy during migration, zspage freeing should
   * hold locks of all pages in the zspage.
   */
  void lock_zspage(struct zspage *zspage)
  {
  	struct page *page = get_first_page(zspage);
  
  	do {
  		lock_page(page);
  	} while ((page = get_next_page(page)) != NULL);
  }
  
  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 = -1 << 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;
  }
  
  #ifdef CONFIG_PGTABLE_MAPPING
  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)
  		return 0;
  	area->vm = alloc_vm_area(PAGE_SIZE * 2, NULL);
  	if (!area->vm)
  		return -ENOMEM;
  	return 0;
  }
  
  static inline void __zs_cpu_down(struct mapping_area *area)
  {
  	if (area->vm)
  		free_vm_area(area->vm);
  	area->vm = NULL;
  }
  
  static inline void *__zs_map_object(struct mapping_area *area,
  				struct page *pages[2], int off, int size)
  {
  	BUG_ON(map_vm_area(area->vm, PAGE_KERNEL, pages));
  	area->vm_addr = area->vm->addr;
  	return area->vm_addr + off;
  }
  
  static inline void __zs_unmap_object(struct mapping_area *area,
  				struct page *pages[2], int off, int size)
  {
  	unsigned long addr = (unsigned long)area->vm_addr;
  
  	unmap_kernel_range(addr, PAGE_SIZE * 2);
  }
  
  #else /* CONFIG_PGTABLE_MAPPING */
  
  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();
  }
  
  #endif /* CONFIG_PGTABLE_MAPPING */
  
  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 void __init init_zs_size_classes(void)
  {
  	int nr;
  
  	nr = (ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) / ZS_SIZE_CLASS_DELTA + 1;
  	if ((ZS_MAX_ALLOC_SIZE - ZS_MIN_ALLOC_SIZE) % ZS_SIZE_CLASS_DELTA)
  		nr += 1;
  
  	zs_size_classes = nr;
  }
  
  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
   *
   * 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.
  	 */
  	WARN_ON_ONCE(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);
  
  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
  static struct dentry *zs_mount(struct file_system_type *fs_type,
  				int flags, const char *dev_name, void *data)
  {
  	static const struct dentry_operations ops = {
  		.d_dname = simple_dname,
  	};
  
  	return mount_pseudo(fs_type, "zsmalloc:", NULL, &ops, ZSMALLOC_MAGIC);
  }
  
  static struct file_system_type zsmalloc_fs = {
  	.name		= "zsmalloc",
  	.mount		= zs_mount,
  	.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)
  {
  	read_lock(&zspage->lock);
  }
  
  static void migrate_read_unlock(struct zspage *zspage)
  {
  	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 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));
  }
  
  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);
  		remove_zspage(class, zspage, fullness);
  	}
  
  	inc_zspage_isolation(zspage);
  	spin_unlock(&class->lock);
  
  	return true;
  }
  
  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;
  
  	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)) {
  		ret = -EBUSY;
  		goto unlock_class;
  	}
  
  	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))
  		putback_zspage(class, zspage);
  
  	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);
  unlock_class:
  	spin_unlock(&class->lock);
  	migrate_write_unlock(zspage);
  
  	return ret;
  }
  
  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)) {
  		fg = putback_zspage(class, zspage);
  		/*
  		 * Due to page_lock, we cannot free zspage immediately
  		 * so let's defer.
  		 */
  		if (fg == ZS_EMPTY)
  			schedule_work(&pool->free_work);
  	}
  	spin_unlock(&class->lock);
  }
  
  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 void zs_unregister_migration(struct zs_pool *pool)
  {
  	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 void __zs_compact(struct zs_pool *pool, struct size_class *class)
  {
  	struct zs_compact_control cc;
  	struct zspage *src_zspage;
  	struct zspage *dst_zspage = NULL;
  
  	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);
  			pool->stats.pages_compacted += 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);
  }
  
  unsigned long zs_compact(struct zs_pool *pool)
  {
  	int i;
  	struct size_class *class;
  
  	for (i = zs_size_classes - 1; i >= 0; i--) {
  		class = pool->size_class[i];
  		if (!class)
  			continue;
  		if (class->index != i)
  			continue;
  		__zs_compact(pool, class);
  	}
  
  	return pool->stats.pages_compacted;
  }
  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);
  
  	pages_freed = pool->stats.pages_compacted;
  	/*
  	 * Compact classes and calculate compaction delta.
  	 * Can run concurrently with a manually triggered
  	 * (by user) compaction.
  	 */
  	pages_freed = zs_compact(pool) - pages_freed;
  
  	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)
  {
  	if (pool->shrinker_enabled) {
  		unregister_shrinker(&pool->shrinker);
  		pool->shrinker_enabled = false;
  	}
  }
  
  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->size_class = kcalloc(zs_size_classes, sizeof(struct size_class *),
  			GFP_KERNEL);
  	if (!pool->size_class) {
  		kfree(pool);
  		return NULL;
  	}
  
  	pool->name = kstrdup(name, GFP_KERNEL);
  	if (!pool->name)
  		goto err;
  
  	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;
  
  		/*
  		 * 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, we still can use the pool
  	 * and user can trigger compaction manually.
  	 */
  	if (zs_register_shrinker(pool) == 0)
  		pool->shrinker_enabled = true;
  	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->size_class);
  	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;
  
  	init_zs_size_classes();
  
  #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>");
  