/*
   * 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 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;
  
  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;
  	/*
  	 * 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

  };

  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 {

  #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 __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 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_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
  ");
  		return;
  	}

  
  	zs_stat_root = debugfs_create_dir("zsmalloc", NULL);
  	if (!zs_stat_root)

  		pr_warn("debugfs 'zsmalloc' stat dir creation failed
  ");

  }
  
  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
  ",

  			"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
  ",

  			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, "
  ");

  	seq_printf(s, " %5s %5s %11lu %12lu %13lu %10lu %10lu %16s %8lu
  ",

  			"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
  ", name);

  		return;

  	}

  
  	entry = debugfs_create_dir(name, zs_stat_root);
  	if (!entry) {
  		pr_warn("debugfs dir <%s> creation failed
  ", 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
  ",
  				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 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.

  	 */

  	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);

  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;