Skip to content
Snippets Groups Projects
Select Git revision
  • 3457f4147675108aa83f9f33c136f06bb9f8518f
  • vme-testing default
  • ci-test
  • master
  • remoteproc
  • am625-sk-ov5640
  • pcal6534-upstreaming
  • lps22df-upstreaming
  • msc-upstreaming
  • imx8mp
  • iio/noa1305
  • vme-next
  • vme-next-4.14-rc4
  • v4.14-rc4
  • v4.14-rc3
  • v4.14-rc2
  • v4.14-rc1
  • v4.13
  • vme-next-4.13-rc7
  • v4.13-rc7
  • v4.13-rc6
  • v4.13-rc5
  • v4.13-rc4
  • v4.13-rc3
  • v4.13-rc2
  • v4.13-rc1
  • v4.12
  • v4.12-rc7
  • v4.12-rc6
  • v4.12-rc5
  • v4.12-rc4
  • v4.12-rc3
32 results

zsmalloc.c

Blame
  • zsmalloc.c 59.29 KiB
    /*
     * 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 + 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(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>");