Re: [PATCH v7 11/12] zsmalloc: page migration support

[Chulmin Kim <cmlaika.kim@samsung.com>]

Hello. Minchan, and all zsmalloc guys.

I have a quick question.
Is zsmalloc considering memory barrier things correctly?

AFAIK, in ARM64,
zsmalloc relies on dmb operation in bit_spin_unlock only.
(It seems that dmb operations in spinlock functions are being prepared,
but let is be aside as it is not merged yet.)

If I am correct,
migrating a page in a zspage filled with free objs
may cause the corruption cause bit_spin_unlock will not be executed at all.

I am not sure this is enough memory barrier for zsmalloc operations.

Can you enlighten me?


THanks!
CHulmin KIm



On 05/31/2016 07:21 PM, Minchan Kim wrote:
> This patch introduces run-time migration feature for zspage.
>
> For migration, VM uses page.lru field so it would be better to not use
> page.next field which is unified with page.lru for own purpose.
> For that, firstly, we can get first object offset of the page via
> runtime calculation instead of using page.index so we can use
> page.index as link for page chaining instead of page.next.
> 	
> In case of huge object, it stores handle to page.index instead of
> next link of page chaining because huge object doesn't need to next
> link for page chaining. So get_next_page need to identify huge
> object to return NULL. For it, this patch uses PG_owner_priv_1 flag
> of the page flag.
>
> For migration, it supports three functions
>
> * zs_page_isolate
>
> It isolates a zspage which includes a subpage VM want to migrate
> from class so anyone cannot allocate new object from the zspage.
>
> We could try to isolate a zspage by the number of subpage so
> subsequent isolation trial of other subpage of the zpsage shouldn't
> fail. For that, we introduce zspage.isolated count. With that,
> zs_page_isolate can know whether zspage is already isolated or not
> for migration so if it is isolated for migration, subsequent
> isolation trial can be successful without trying further isolation.
>
> * zs_page_migrate
>
> First of all, it holds write-side zspage->lock to prevent migrate other
> subpage in zspage. Then, lock all objects in the page VM want to migrate.
> The reason we should lock all objects in the page is due to race between
> zs_map_object and zs_page_migrate.
>
> zs_map_object				zs_page_migrate
>
> pin_tag(handle)
> obj = handle_to_obj(handle)
> obj_to_location(obj, &page, &obj_idx);
>
> 					write_lock(&zspage->lock)
> 					if (!trypin_tag(handle))
> 						goto unpin_object
>
> zspage = get_zspage(page);
> read_lock(&zspage->lock);
>
> If zs_page_migrate doesn't do trypin_tag, zs_map_object's page can
> be stale by migration so it goes crash.
>
> If it locks all of objects successfully, it copies content from
> old page to new one, finally, create new zspage chain with new page.
> And if it's last isolated subpage in the zspage, put the zspage back
> to class.
>
> * zs_page_putback
>
> It returns isolated zspage to right fullness_group list if it fails to
> migrate a page. If it find a zspage is ZS_EMPTY, it queues zspage
> freeing to workqueue. See below about async zspage freeing.
>
> This patch introduces asynchronous zspage free. The reason to need it
> is we need page_lock to clear PG_movable but unfortunately,
> zs_free path should be atomic so the apporach is try to grab page_lock.
> If it got page_lock of all of pages successfully, it can free zspage
> immediately. Otherwise, it queues free request and free zspage via
> workqueue in process context.
>
> If zs_free finds the zspage is isolated when it try to free zspage,
> it delays the freeing until zs_page_putback finds it so it will free
> free the zspage finally.
>
> In this patch, we expand fullness_list from ZS_EMPTY to ZS_FULL.
> First of all, it will use ZS_EMPTY list for delay freeing.
> And with adding ZS_FULL list, it makes to identify whether zspage is
> isolated or not via list_empty(&zspage->list) test.
>
> Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
>  include/uapi/linux/magic.h |   1 +
>  mm/zsmalloc.c              | 793 ++++++++++++++++++++++++++++++++++++++-------
>  2 files changed, 672 insertions(+), 122 deletions(-)
>
> diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
> index d829ce63529d..e398beac67b8 100644
> --- a/include/uapi/linux/magic.h
> +++ b/include/uapi/linux/magic.h
> @@ -81,5 +81,6 @@
>  /* Since UDF 2.01 is ISO 13346 based... */
>  #define UDF_SUPER_MAGIC		0x15013346
>  #define BALLOON_KVM_MAGIC	0x13661366
> +#define ZSMALLOC_MAGIC		0x58295829
>
>  #endif /* __LINUX_MAGIC_H__ */
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index c6fb543cfb98..a80100db16d6 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -17,14 +17,14 @@
>   *
>   * Usage of struct page fields:
>   *	page->private: points to zspage
> - *	page->index: offset of the first object starting in this page.
> - *		For the first page, this is always 0, so we use this field
> - *		to store handle for huge object.
> - *	page->next: links together all component pages of a 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.
>   *
>   * Usage of struct page flags:
>   *	PG_private: identifies the first component page
>   *	PG_private2: identifies the last component page
> + *	PG_owner_priv_1: indentifies the huge component page
>   *
>   */
>
> @@ -49,6 +49,11 @@
>  #include <linux/debugfs.h>
>  #include <linux/zsmalloc.h>
>  #include <linux/zpool.h>
> +#include <linux/mount.h>
> +#include <linux/compaction.h>
> +#include <linux/pagemap.h>
> +
> +#define ZSPAGE_MAGIC	0x58
>
>  /*
>   * This must be power of 2 and greater than of equal to sizeof(link_free).
> @@ -136,25 +141,23 @@
>   * We do not maintain any list for completely empty or full pages
>   */
>  enum fullness_group {
> -	ZS_ALMOST_FULL,
> -	ZS_ALMOST_EMPTY,
>  	ZS_EMPTY,
> -	ZS_FULL
> +	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,
> -	CLASS_ALMOST_FULL,
> -	CLASS_ALMOST_EMPTY,
> +	NR_ZS_STAT_TYPE,
>  };
>
> -#ifdef CONFIG_ZSMALLOC_STAT
> -#define NR_ZS_STAT_TYPE	(CLASS_ALMOST_EMPTY + 1)
> -#else
> -#define NR_ZS_STAT_TYPE	(OBJ_USED + 1)
> -#endif
> -
>  struct zs_size_stat {
>  	unsigned long objs[NR_ZS_STAT_TYPE];
>  };
> @@ -163,6 +166,10 @@ struct zs_size_stat {
>  static struct dentry *zs_stat_root;
>  #endif
>
> +#ifdef CONFIG_COMPACTION
> +static struct vfsmount *zsmalloc_mnt;
> +#endif
> +
>  /*
>   * number of size_classes
>   */
> @@ -186,23 +193,36 @@ static const int fullness_threshold_frac = 4;
>
>  struct size_class {
>  	spinlock_t lock;
> -	struct list_head fullness_list[2];
> +	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;
> -	unsigned int index;
> -
> -	struct zs_size_stat stats;
> -
>  	/* Number of PAGE_SIZE sized pages to combine to form a 'zspage' */
>  	int pages_per_zspage;
> -	/* huge object: pages_per_zspage == 1 && maxobj_per_zspage == 1 */
> -	bool huge;
> +
> +	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.
> @@ -244,6 +264,10 @@ struct zs_pool {
>  #ifdef CONFIG_ZSMALLOC_STAT
>  	struct dentry *stat_dentry;
>  #endif
> +#ifdef CONFIG_COMPACTION
> +	struct inode *inode;
> +	struct work_struct free_work;
> +#endif
>  };
>
>  /*
> @@ -252,16 +276,23 @@ struct zs_pool {
>   */
>  #define FULLNESS_BITS	2
>  #define CLASS_BITS	8
> +#define ISOLATED_BITS	3
> +#define MAGIC_VAL_BITS	8
>
>  struct zspage {
>  	struct {
>  		unsigned int fullness:FULLNESS_BITS;
>  		unsigned int class:CLASS_BITS;
> +		unsigned int isolated:ISOLATED_BITS;
> +		unsigned int magic:MAGIC_VAL_BITS;
>  	};
>  	unsigned int inuse;
>  	unsigned int freeobj;
>  	struct page *first_page;
>  	struct list_head list; /* fullness list */
> +#ifdef CONFIG_COMPACTION
> +	rwlock_t lock;
> +#endif
>  };
>
>  struct mapping_area {
> @@ -274,6 +305,28 @@ struct mapping_area {
>  	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,
> @@ -301,7 +354,7 @@ static void destroy_cache(struct zs_pool *pool)
>  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 & ~(__GFP_HIGHMEM|__GFP_MOVABLE));
>  }
>
>  static void cache_free_handle(struct zs_pool *pool, unsigned long handle)
> @@ -311,7 +364,8 @@ static void cache_free_handle(struct zs_pool *pool, unsigned long handle)
>
>  static struct zspage *cache_alloc_zspage(struct zs_pool *pool, gfp_t flags)
>  {
> -	return kmem_cache_alloc(pool->zspage_cachep, flags & ~__GFP_HIGHMEM);
> +	return kmem_cache_alloc(pool->zspage_cachep,
> +			flags & ~(__GFP_HIGHMEM|__GFP_MOVABLE));
>  };
>
>  static void cache_free_zspage(struct zs_pool *pool, struct zspage *zspage)
> @@ -421,11 +475,17 @@ static unsigned int get_maxobj_per_zspage(int size, int pages_per_zspage)
>  /* per-cpu VM mapping areas for zspage accesses that cross page boundaries */
>  static DEFINE_PER_CPU(struct mapping_area, zs_map_area);
>
> +static bool is_zspage_isolated(struct zspage *zspage)
> +{
> +	return zspage->isolated;
> +}
> +
>  static int is_first_page(struct page *page)
>  {
>  	return PagePrivate(page);
>  }
>
> +/* Protected by class->lock */
>  static inline int get_zspage_inuse(struct zspage *zspage)
>  {
>  	return zspage->inuse;
> @@ -441,20 +501,12 @@ static inline void mod_zspage_inuse(struct zspage *zspage, int val)
>  	zspage->inuse += val;
>  }
>
> -static inline int get_first_obj_offset(struct page *page)
> +static inline struct page *get_first_page(struct zspage *zspage)
>  {
> -	if (is_first_page(page))
> -		return 0;
> +	struct page *first_page = zspage->first_page;
>
> -	return page->index;
> -}
> -
> -static inline void set_first_obj_offset(struct page *page, int offset)
> -{
> -	if (is_first_page(page))
> -		return;
> -
> -	page->index = offset;
> +	VM_BUG_ON_PAGE(!is_first_page(first_page), first_page);
> +	return first_page;
>  }
>
>  static inline unsigned int get_freeobj(struct zspage *zspage)
> @@ -471,6 +523,8 @@ static void get_zspage_mapping(struct zspage *zspage,
>  				unsigned int *class_idx,
>  				enum fullness_group *fullness)
>  {
> +	VM_BUG_ON(zspage->magic != ZSPAGE_MAGIC);
> +
>  	*fullness = zspage->fullness;
>  	*class_idx = zspage->class;
>  }
> @@ -504,23 +558,19 @@ static int get_size_class_index(int size)
>  static inline void zs_stat_inc(struct size_class *class,
>  				enum zs_stat_type type, unsigned long cnt)
>  {
> -	if (type < NR_ZS_STAT_TYPE)
> -		class->stats.objs[type] += cnt;
> +	class->stats.objs[type] += cnt;
>  }
>
>  static inline void zs_stat_dec(struct size_class *class,
>  				enum zs_stat_type type, unsigned long cnt)
>  {
> -	if (type < NR_ZS_STAT_TYPE)
> -		class->stats.objs[type] -= cnt;
> +	class->stats.objs[type] -= cnt;
>  }
>
>  static inline unsigned long zs_stat_get(struct size_class *class,
>  				enum zs_stat_type type)
>  {
> -	if (type < NR_ZS_STAT_TYPE)
> -		return class->stats.objs[type];
> -	return 0;
> +	return class->stats.objs[type];
>  }
>
>  #ifdef CONFIG_ZSMALLOC_STAT
> @@ -664,6 +714,7 @@ 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
> @@ -704,15 +755,9 @@ static void insert_zspage(struct size_class *class,
>  {
>  	struct zspage *head;
>
> -	if (fullness >= ZS_EMPTY)
> -		return;
> -
> +	zs_stat_inc(class, fullness, 1);
>  	head = list_first_entry_or_null(&class->fullness_list[fullness],
>  					struct zspage, list);
> -
> -	zs_stat_inc(class, fullness == ZS_ALMOST_EMPTY ?
> -			CLASS_ALMOST_EMPTY : CLASS_ALMOST_FULL, 1);
> -
>  	/*
>  	 * We want to see more ZS_FULL pages and less almost empty/full.
>  	 * Put pages with higher ->inuse first.
> @@ -734,14 +779,11 @@ static void remove_zspage(struct size_class *class,
>  				struct zspage *zspage,
>  				enum fullness_group fullness)
>  {
> -	if (fullness >= ZS_EMPTY)
> -		return;
> -
>  	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 == ZS_ALMOST_EMPTY ?
> -			CLASS_ALMOST_EMPTY : CLASS_ALMOST_FULL, 1);
> +	zs_stat_dec(class, fullness, 1);
>  }
>
>  /*
> @@ -764,8 +806,11 @@ static enum fullness_group fix_fullness_group(struct size_class *class,
>  	if (newfg == currfg)
>  		goto out;
>
> -	remove_zspage(class, zspage, currfg);
> -	insert_zspage(class, zspage, newfg);
> +	if (!is_zspage_isolated(zspage)) {
> +		remove_zspage(class, zspage, currfg);
> +		insert_zspage(class, zspage, newfg);
> +	}
> +
>  	set_zspage_mapping(zspage, class_idx, newfg);
>
>  out:
> @@ -808,19 +853,45 @@ static int get_pages_per_zspage(int class_size)
>  	return max_usedpc_order;
>  }
>
> -static struct page *get_first_page(struct zspage *zspage)
> +static struct zspage *get_zspage(struct page *page)
>  {
> -	return zspage->first_page;
> +	struct zspage *zspage = (struct zspage *)page->private;
> +
> +	VM_BUG_ON(zspage->magic != ZSPAGE_MAGIC);
> +	return zspage;
>  }
>
> -static struct zspage *get_zspage(struct page *page)
> +static struct page *get_next_page(struct page *page)
>  {
> -	return (struct zspage *)page->private;
> +	if (unlikely(PageHugeObject(page)))
> +		return NULL;
> +
> +	return page->freelist;
>  }
>
> -static struct page *get_next_page(struct page *page)
> +/* Get byte offset of first object in the @page */
> +static int get_first_obj_offset(struct size_class *class,
> +				struct page *first_page, struct page *page)
>  {
> -	return page->next;
> +	int pos;
> +	int page_idx = 0;
> +	int ofs = 0;
> +	struct page *cursor = first_page;
> +
> +	if (first_page == page)
> +		goto out;
> +
> +	while (page != cursor) {
> +		page_idx++;
> +		cursor = get_next_page(cursor);
> +	}
> +
> +	pos = class->objs_per_zspage * class->size *
> +		page_idx / class->pages_per_zspage;
> +
> +	ofs = (pos + class->size) % PAGE_SIZE;
> +out:
> +	return ofs;
>  }
>
>  /**
> @@ -857,16 +928,20 @@ static unsigned long handle_to_obj(unsigned long handle)
>  	return *(unsigned long *)handle;
>  }
>
> -static unsigned long obj_to_head(struct size_class *class, struct page *page,
> -			void *obj)
> +static unsigned long obj_to_head(struct page *page, void *obj)
>  {
> -	if (class->huge) {
> +	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);
> @@ -884,27 +959,93 @@ static void unpin_tag(unsigned long handle)
>
>  static void reset_page(struct page *page)
>  {
> +	__ClearPageMovable(page);
>  	clear_bit(PG_private, &page->flags);
>  	clear_bit(PG_private_2, &page->flags);
>  	set_page_private(page, 0);
> -	page->index = 0;
> +	ClearPageHugeObject(page);
> +	page->freelist = NULL;
>  }
>
> -static void free_zspage(struct zs_pool *pool, struct zspage *zspage)
> +/*
> + * 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 = zspage->first_page;
> +	next = page = get_first_page(zspage);
>  	do {
> -		next = page->next;
> +		VM_BUG_ON_PAGE(!PageLocked(page), page);
> +		next = get_next_page(page);
>  		reset_page(page);
> +		unlock_page(page);
>  		put_page(page);
>  		page = next;
>  	} while (page != NULL);
>
>  	cache_free_zspage(pool, zspage);
> +
> +	zs_stat_dec(class, OBJ_ALLOCATED, get_maxobj_per_zspage(
> +			class->size, class->pages_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 */
> @@ -912,15 +1053,13 @@ static void init_zspage(struct size_class *class, struct zspage *zspage)
>  {
>  	unsigned int freeobj = 1;
>  	unsigned long off = 0;
> -	struct page *page = zspage->first_page;
> +	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);
>
> @@ -952,16 +1091,17 @@ static void init_zspage(struct size_class *class, struct zspage *zspage)
>  	set_freeobj(zspage, 0);
>  }
>
> -static void create_page_chain(struct zspage *zspage, struct page *pages[],
> -				int nr_pages)
> +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->next
> +	 * 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
> @@ -970,16 +1110,18 @@ static void create_page_chain(struct zspage *zspage, struct page *pages[],
>  	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->next = page;
> +			prev_page->freelist = page;
>  		}
> -		if (i == nr_pages - 1) {
> +		if (i == nr_pages - 1)
>  			SetPagePrivate2(page);
> -			page->next = NULL;
> -		}
>  		prev_page = page;
>  	}
>  }
> @@ -999,6 +1141,8 @@ static struct zspage *alloc_zspage(struct zs_pool *pool,
>  		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;
> @@ -1013,7 +1157,7 @@ static struct zspage *alloc_zspage(struct zs_pool *pool,
>  		pages[i] = page;
>  	}
>
> -	create_page_chain(zspage, pages, class->pages_per_zspage);
> +	create_page_chain(class, zspage, pages);
>  	init_zspage(class, zspage);
>
>  	return zspage;
> @@ -1024,7 +1168,7 @@ static struct zspage *find_get_zspage(struct size_class *class)
>  	int i;
>  	struct zspage *zspage;
>
> -	for (i = ZS_ALMOST_FULL; i <= ZS_ALMOST_EMPTY; i++) {
> +	for (i = ZS_ALMOST_FULL; i >= ZS_EMPTY; i--) {
>  		zspage = list_first_entry_or_null(&class->fullness_list[i],
>  				struct zspage, list);
>  		if (zspage)
> @@ -1289,6 +1433,10 @@ void *zs_map_object(struct zs_pool *pool, unsigned long 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;
> @@ -1309,7 +1457,7 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
>
>  	ret = __zs_map_object(area, pages, off, class->size);
>  out:
> -	if (!class->huge)
> +	if (likely(!PageHugeObject(page)))
>  		ret += ZS_HANDLE_SIZE;
>
>  	return ret;
> @@ -1348,6 +1496,8 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
>  		__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);
> @@ -1377,7 +1527,7 @@ static unsigned long obj_malloc(struct size_class *class,
>  	vaddr = kmap_atomic(m_page);
>  	link = (struct link_free *)vaddr + m_offset / sizeof(*link);
>  	set_freeobj(zspage, link->next >> OBJ_ALLOCATED_TAG);
> -	if (!class->huge)
> +	if (likely(!PageHugeObject(m_page)))
>  		/* record handle in the header of allocated chunk */
>  		link->handle = handle;
>  	else
> @@ -1407,6 +1557,7 @@ 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))
> @@ -1422,28 +1573,37 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t gfp)
>
>  	spin_lock(&class->lock);
>  	zspage = find_get_zspage(class);
> -
> -	if (!zspage) {
> +	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);
> -		zspage = alloc_zspage(pool, class, gfp);
> -		if (unlikely(!zspage)) {
> -			cache_free_handle(pool, handle);
> -			return 0;
> -		}
>
> -		set_zspage_mapping(zspage, class->index, ZS_EMPTY);
> -		atomic_long_add(class->pages_per_zspage,
> -					&pool->pages_allocated);
> +		return handle;
> +	}
>
> -		spin_lock(&class->lock);
> -		zs_stat_inc(class, OBJ_ALLOCATED, get_maxobj_per_zspage(
> -				class->size, class->pages_per_zspage));
> +	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);
> -	/* Now move the zspage to another fullness group, if required */
> -	fix_fullness_group(class, zspage);
> +	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, get_maxobj_per_zspage(
> +			class->size, class->pages_per_zspage));
> +
> +	/* We completely set up zspage so mark them as movable */
> +	SetZsPageMovable(pool, zspage);
>  	spin_unlock(&class->lock);
>
>  	return handle;
> @@ -1484,6 +1644,7 @@ void zs_free(struct zs_pool *pool, unsigned long handle)
>  	int class_idx;
>  	struct size_class *class;
>  	enum fullness_group fullness;
> +	bool isolated;
>
>  	if (unlikely(!handle))
>  		return;
> @@ -1493,22 +1654,28 @@ void zs_free(struct zs_pool *pool, unsigned long 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) {
> -		zs_stat_dec(class, OBJ_ALLOCATED, get_maxobj_per_zspage(
> -				class->size, class->pages_per_zspage));
> -		atomic_long_sub(class->pages_per_zspage,
> -				&pool->pages_allocated);
> -		free_zspage(pool, 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);
> @@ -1587,12 +1754,13 @@ static unsigned long find_alloced_obj(struct size_class *class,
>  	int offset = 0;
>  	unsigned long handle = 0;
>  	void *addr = kmap_atomic(page);
> +	struct zspage *zspage = get_zspage(page);
>
> -	offset = get_first_obj_offset(page);
> +	offset = get_first_obj_offset(class, get_first_page(zspage), page);
>  	offset += class->size * index;
>
>  	while (offset < PAGE_SIZE) {
> -		head = obj_to_head(class, page, addr + offset);
> +		head = obj_to_head(page, addr + offset);
>  		if (head & OBJ_ALLOCATED_TAG) {
>  			handle = head & ~OBJ_ALLOCATED_TAG;
>  			if (trypin_tag(handle))
> @@ -1684,6 +1852,7 @@ static struct zspage *isolate_zspage(struct size_class *class, bool source)
>  		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;
>  		}
> @@ -1704,6 +1873,8 @@ static enum fullness_group putback_zspage(struct size_class *class,
>  {
>  	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);
> @@ -1711,6 +1882,377 @@ static enum fullness_group putback_zspage(struct size_class *class,
>  	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);
> +	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(class, get_first_page(zspage), 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 = 0;
> +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);
> +	if (pool->inode)
> +		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
> @@ -1745,10 +2287,10 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class)
>  			break;
>
>  		cc.index = 0;
> -		cc.s_page = src_zspage->first_page;
> +		cc.s_page = get_first_page(src_zspage);
>
>  		while ((dst_zspage = isolate_zspage(class, false))) {
> -			cc.d_page = dst_zspage->first_page;
> +			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.
> @@ -1765,11 +2307,7 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class)
>
>  		putback_zspage(class, dst_zspage);
>  		if (putback_zspage(class, src_zspage) == ZS_EMPTY) {
> -			zs_stat_dec(class, OBJ_ALLOCATED, get_maxobj_per_zspage(
> -					class->size, class->pages_per_zspage));
> -			atomic_long_sub(class->pages_per_zspage,
> -					&pool->pages_allocated);
> -			free_zspage(pool, src_zspage);
> +			free_zspage(pool, class, src_zspage);
>  			pool->stats.pages_compacted += class->pages_per_zspage;
>  		}
>  		spin_unlock(&class->lock);
> @@ -1885,6 +2423,7 @@ struct zs_pool *zs_create_pool(const char *name)
>  	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) {
> @@ -1939,12 +2478,10 @@ struct zs_pool *zs_create_pool(const char *name)
>  		class->pages_per_zspage = pages_per_zspage;
>  		class->objs_per_zspage = class->pages_per_zspage *
>  						PAGE_SIZE / class->size;
> -		if (pages_per_zspage == 1 && class->objs_per_zspage == 1)
> -			class->huge = true;
>  		spin_lock_init(&class->lock);
>  		pool->size_class[i] = class;
> -		for (fullness = ZS_ALMOST_FULL; fullness <= ZS_ALMOST_EMPTY;
> -								fullness++)
> +		for (fullness = ZS_EMPTY; fullness < NR_ZS_FULLNESS;
> +							fullness++)
>  			INIT_LIST_HEAD(&class->fullness_list[fullness]);
>
>  		prev_class = class;
> @@ -1953,6 +2490,9 @@ struct zs_pool *zs_create_pool(const char *name)
>  	/* 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.
> @@ -1972,6 +2512,7 @@ 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++) {
> @@ -1984,7 +2525,7 @@ void zs_destroy_pool(struct zs_pool *pool)
>  		if (class->index != i)
>  			continue;
>
> -		for (fg = ZS_ALMOST_FULL; fg <= ZS_ALMOST_EMPTY; fg++) {
> +		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);
> @@ -2002,7 +2543,13 @@ EXPORT_SYMBOL_GPL(zs_destroy_pool);
>
>  static int __init zs_init(void)
>  {
> -	int ret = zs_register_cpu_notifier();
> +	int ret;
> +
> +	ret = zsmalloc_mount();
> +	if (ret)
> +		goto out;
> +
> +	ret = zs_register_cpu_notifier();
>
>  	if (ret)
>  		goto notifier_fail;
> @@ -2019,7 +2566,8 @@ static int __init zs_init(void)
>
>  notifier_fail:
>  	zs_unregister_cpu_notifier();
> -
> +	zsmalloc_unmount();
> +out:
>  	return ret;
>  }
>
> @@ -2028,6 +2576,7 @@ static void __exit zs_exit(void)
>  #ifdef CONFIG_ZPOOL
>  	zpool_unregister_driver(&zs_zpool_driver);
>  #endif
> +	zsmalloc_unmount();
>  	zs_unregister_cpu_notifier();
>
>  	zs_stat_exit();
>

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