Message-ID: <20160503004359.GA2272@bbox>
Date:	Tue, 3 May 2016 09:43:59 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Chulmin Kim <cmlaika.kim@...sung.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [PATCH v4 11/12] zsmalloc: page migration support

Good morning, Chulmin

On Tue, May 03, 2016 at 08:33:16AM +0900, Chulmin Kim wrote:
> Hello, Minchan!
> 
> On 2016년 04월 27일 16:48, 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 for own purpose. For that, firstly, we can get first
> >object offset of the page via runtime calculation instead of
> >page->index so we can use page->index as link for page chaining.
> >In case of huge object, it stores handle rather than page chaining.
> >To identify huge object, we uses PG_owner_priv_1 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 if it's first
> >isolation on subpages of zspage. Thus, further isolation on other
> >subpages cannot isolate zspage from class list.
> >
> >* 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 so go crash.
> >
> >If it locks all of objects successfully, it copies content from old page
> >create new one, finally, create new page chain with new page.
> >If it's last isolated page 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.
> >
> >Lastly, this patch introduces asynchronous zspage free. The reason
> >we 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
> >with preemption disabled. If it got page_lock of all of pages
> >successfully, it can free zspage in the context. Otherwise, it queues
> >the free request and free zspage via workqueue in process context.
> >
> >Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> >Signed-off-by: Minchan Kim <minchan@...nel.org>
> >---
> >  include/uapi/linux/magic.h |   1 +
> >  mm/zsmalloc.c              | 552 +++++++++++++++++++++++++++++++++++++++------
> >  2 files changed, 487 insertions(+), 66 deletions(-)
> >
> >diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
> >index e1fbe72c39c0..93b1affe4801 100644
> >--- a/include/uapi/linux/magic.h
> >+++ b/include/uapi/linux/magic.h
> >@@ -79,5 +79,6 @@
> >  #define NSFS_MAGIC		0x6e736673
> >  #define BPF_FS_MAGIC		0xcafe4a11
> >  #define BALLOON_KVM_MAGIC	0x13661366
> >+#define ZSMALLOC_MAGIC		0x58295829
> >
> >  #endif /* __LINUX_MAGIC_H__ */
> >diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> >index 8d82e44c4644..042793015ecf 100644
> >--- a/mm/zsmalloc.c
> >+++ b/mm/zsmalloc.c
> >@@ -17,15 +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: 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
> >   */
> >
> >  #include <linux/module.h>
> >@@ -47,6 +46,10 @@
> >  #include <linux/debugfs.h>
> >  #include <linux/zsmalloc.h>
> >  #include <linux/zpool.h>
> >+#include <linux/mount.h>
> >+#include <linux/migrate.h>
> >+
> >+#define ZSPAGE_MAGIC	0x58
> >
> >  /*
> >   * This must be power of 2 and greater than of equal to sizeof(link_free).
> >@@ -128,8 +131,33 @@
> >   *  ZS_MIN_ALLOC_SIZE and ZS_SIZE_CLASS_DELTA must be multiple of ZS_ALIGN
> >   *  (reason above)
> >   */
> >+
> >+/*
> >+ * A zspage's class index and fullness group
> >+ * are encoded in its (first)page->mapping
> >+ */
> >+#define FULLNESS_BITS	2
> >+#define CLASS_BITS	8
> >+#define ISOLATED_BITS	3
> >+#define MAGIC_VAL_BITS	8
> >+
> >+
> >  #define ZS_SIZE_CLASS_DELTA	(PAGE_SIZE >> CLASS_BITS)
> >
> >+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 */
> >+	rwlock_t lock;
> >+};
> >+
> >  /*
> >   * We do not maintain any list for completely empty or full pages
> >   */
> >@@ -161,6 +189,8 @@ struct zs_size_stat {
> >  static struct dentry *zs_stat_root;
> >  #endif
> >
> >+static struct vfsmount *zsmalloc_mnt;
> >+
> >  /*
> >   * number of size_classes
> >   */
> >@@ -243,24 +273,10 @@ struct zs_pool {
> >  #ifdef CONFIG_ZSMALLOC_STAT
> >  	struct dentry *stat_dentry;
> >  #endif
> >-};
> >-
> >-/*
> >- * A zspage's class index and fullness group
> >- * are encoded in its (first)page->mapping
> >- */
> >-#define FULLNESS_BITS	2
> >-#define CLASS_BITS	8
> >-
> >-struct zspage {
> >-	struct {
> >-		unsigned int fullness:FULLNESS_BITS;
> >-		unsigned int class:CLASS_BITS;
> >-	};
> >-	unsigned int inuse;
> >-	unsigned int freeobj;
> >-	struct page *first_page;
> >-	struct list_head list; /* fullness list */
> >+	struct inode *inode;
> >+	spinlock_t free_lock;
> >+	struct work_struct free_work;
> >+	struct list_head free_zspage;
> >  };
> >
> >  struct mapping_area {
> >@@ -312,8 +328,11 @@ static struct zspage *cache_alloc_zspage(struct zs_pool *pool, gfp_t flags)
> >  	struct zspage *zspage;
> >
> >  	zspage = kmem_cache_alloc(pool->zspage_cachep, flags & ~__GFP_HIGHMEM);
> >-	if (zspage)
> >+	if (zspage) {
> >  		memset(zspage, 0, sizeof(struct zspage));
> >+		zspage->magic = ZSPAGE_MAGIC;
> >+		rwlock_init(&zspage->lock);
> 
> +              INIT_LIST_HEAD(&zspage->list);
> 
> If there is no special intention here,
> I think we need the list initialization.

Intention was that I just watned to add unncessary instruction there
although it was not expensive. :)

> 
> There are some functions checking "list_empty(&zspage->list)".
> and they might be executed before the list initialization in rare cases.

There are two places now.

1. zspage_isolate

It's okay because zs_page_isolate checks get_zspage_inuse under
class->lock while alloc_zspage adds newly created zspage to list
under class->lock with increasing used object count.

2. free_zspage

It's okay because every zspage passed free_zspage should
remove from list and remove_zspage has list_del_init and
the used object in the zspage should be zero so zs_page_isolate
cannot pick it up.

> (AFAIK, the list initialization is being done by insert_zspage(),etc.)
> I guess, checking the uninitialized list is not intended at all.

You have been great to spot something until now so you are saying
with some clue already and I might miss something. :)

Do you have another scenario to make race problem?
Otherwise, I want to remain as it is because I want to reveal the
problem rather than hiding problems with safe-guard. :)

Thanks for the review, Chulmin!
> 
> Thanks!
> Chulmin
> 
> 
> >+	}
> >  	return zspage;
> >  };
> >
> >@@ -419,11 +438,27 @@ 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 void inc_zspage_isolation(struct zspage *zspage)
> >+{
> >+	zspage->isolated++;
> >+}
> >+
> >+static void dec_zspage_isolation(struct zspage *zspage)
> >+{
> >+	zspage->isolated--;
> >+}
> >+
> >+static int get_zspage_isolation(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;
> >@@ -439,20 +474,12 @@ 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)
> >@@ -469,6 +496,8 @@ 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;
> >  }
> >@@ -738,6 +767,7 @@ static void remove_zspage(struct size_class *class,
> >  		return;
> >
> >  	VM_BUG_ON(list_empty(&class->fullness_list[fullness]));
> >+	VM_BUG_ON(get_zspage_isolation(zspage));
> >
> >  	list_del_init(&zspage->list);
> >  	zs_stat_dec(class, fullness == ZS_ALMOST_EMPTY ?
> >@@ -764,8 +794,10 @@ 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 (!get_zspage_isolation(zspage)) {
> >+		remove_zspage(class, zspage, currfg);
> >+		insert_zspage(class, zspage, newfg);
> >+	}
> >  	set_zspage_mapping(zspage, class_idx, newfg);
> >
> >  out:
> >@@ -808,19 +840,47 @@ 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 (PageOwnerPriv1(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, bound;
> >+	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);
> >+	}
> >+
> >+	bound = PAGE_SIZE * page_idx;
> >+	pos = (((class->objs_per_zspage * class->size) *
> >+		page_idx / class->pages_per_zspage) / class->size
> >+	      ) * class->size;
> >+
> >+	ofs = (pos + class->size) % PAGE_SIZE;
> >+out:
> >+	return ofs;
> >  }
> >
> >  /**
> >@@ -867,6 +927,11 @@ static unsigned long obj_to_head(struct size_class *class, struct page *page,
> >  		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);
> >@@ -884,22 +949,60 @@ 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);
> >+	ClearPageOwnerPriv1(page);
> >  	set_page_private(page, 0);
> >-	page->index = 0;
> >+	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 zspage *zspage)
> >  {
> >  	struct page *page, *next;
> >
> >  	VM_BUG_ON(get_zspage_inuse(zspage));
> >
> >-	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);
> >@@ -907,20 +1010,34 @@ static void free_zspage(struct zs_pool *pool, struct zspage *zspage)
> >  	cache_free_zspage(pool, zspage);
> >  }
> >
> >+static void free_zspage(struct zs_pool *pool, struct zspage *zspage)
> >+{
> >+	VM_BUG_ON(get_zspage_inuse(zspage));
> >+
> >+	if (!trylock_zspage(zspage)) {
> >+		spin_lock(&pool->free_lock);
> >+		VM_BUG_ON(!list_empty(&zspage->list));
> >+		list_add(&zspage->list, &pool->free_zspage);
> >+		spin_unlock(&pool->free_lock);
> >+		schedule_work(&pool->free_work);
> >+		return;
> >+	}
> >+
> >+	__free_zspage(pool, 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 = 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 +1069,17 @@ 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
> >@@ -970,20 +1088,43 @@ 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 (class->huge)
> >+				SetPageOwnerPriv1(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;
> >  	}
> >  }
> >
> >+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 (class->huge)
> >+		newpage->index = oldpage->index;
> >+	__SetPageMovable(newpage, page_mapping(oldpage));
> >+}
> >+
> >  /*
> >   * Allocate a zspage for the given size class
> >   */
> >@@ -1010,7 +1151,7 @@ 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;
> >@@ -1286,6 +1427,10 @@ 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 */
> >+	read_lock(&zspage->lock);
> >+
> >  	get_zspage_mapping(zspage, &class_idx, &fg);
> >  	class = pool->size_class[class_idx];
> >  	off = (class->size * obj_idx) & ~PAGE_MASK;
> >@@ -1345,6 +1490,8 @@ 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);
> >+
> >+	read_unlock(&zspage->lock);
> >  	unpin_tag(handle);
> >  }
> >  EXPORT_SYMBOL_GPL(zs_unmap_object);
> >@@ -1421,6 +1568,8 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
> >  	zspage = find_get_zspage(class);
> >
> >  	if (!zspage) {
> >+		struct page *page;
> >+
> >  		spin_unlock(&class->lock);
> >  		zspage = alloc_zspage(pool, class);
> >  		if (unlikely(!zspage)) {
> >@@ -1432,6 +1581,14 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size)
> >  		atomic_long_add(class->pages_per_zspage,
> >  					&pool->pages_allocated);
> >
> >+		/* We completely set up zspage so mark them as movable */
> >+		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);
> >+
> >  		spin_lock(&class->lock);
> >  		zs_stat_inc(class, OBJ_ALLOCATED, get_maxobj_per_zspage(
> >  				class->size, class->pages_per_zspage));
> >@@ -1490,6 +1647,8 @@ void zs_free(struct zs_pool *pool, unsigned long handle)
> >  	obj_to_location(obj, &f_page, &f_objidx);
> >  	zspage = get_zspage(f_page);
> >
> >+	read_lock(&zspage->lock);
> >+
> >  	get_zspage_mapping(zspage, &class_idx, &fullness);
> >  	class = pool->size_class[class_idx];
> >
> >@@ -1501,11 +1660,14 @@ void zs_free(struct zs_pool *pool, unsigned long handle)
> >  				class->size, class->pages_per_zspage));
> >  		atomic_long_sub(class->pages_per_zspage,
> >  				&pool->pages_allocated);
> >+		read_unlock(&zspage->lock);
> >  		free_zspage(pool, zspage);
> >+		spin_unlock(&class->lock);
> >+	} else {
> >+		read_unlock(&zspage->lock);
> >+		spin_unlock(&class->lock);
> >  	}
> >-	spin_unlock(&class->lock);
> >  	unpin_tag(handle);
> >-
> >  	cache_free_handle(pool, handle);
> >  }
> >  EXPORT_SYMBOL_GPL(zs_free);
> >@@ -1584,8 +1746,9 @@ 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) {
> >@@ -1681,6 +1844,7 @@ 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(get_zspage_isolation(zspage));
> >  			remove_zspage(class, zspage, fg[i]);
> >  			return zspage;
> >  		}
> >@@ -1701,6 +1865,8 @@ static enum fullness_group putback_zspage(struct size_class *class,
> >  {
> >  	enum fullness_group fullness;
> >
> >+	VM_BUG_ON(get_zspage_isolation(zspage));
> >+
> >  	fullness = get_fullness_group(class, zspage);
> >  	insert_zspage(class, zspage, fullness);
> >  	set_zspage_mapping(zspage, class->index, fullness);
> >@@ -1739,10 +1905,10 @@ 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.
> >@@ -1859,6 +2025,218 @@ static int zs_register_shrinker(struct zs_pool *pool)
> >  	return register_shrinker(&pool->shrinker);
> >  }
> >
> >+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) && !get_zspage_isolation(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) && !get_zspage_isolation(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 */
> >+	write_lock(&zspage->lock);
> >+	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))
> >+		goto unlock_class;
> >+
> >+	pos = offset;
> >+	s_addr = kmap_atomic(page);
> >+	while (pos < PAGE_SIZE) {
> >+		head = obj_to_head(class, 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(class, 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 (!get_zspage_isolation(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(class, 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);
> >+	write_unlock(&zspage->lock);
> >+
> >+	return ret;
> >+}
> >+
> >+void zs_page_putback(struct page *page)
> >+{
> >+	struct zs_pool *pool;
> >+	struct size_class *class;
> >+	int class_idx;
> >+	enum fullness_group dummy;
> >+	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, &dummy);
> >+	mapping = page_mapping(page);
> >+	pool = mapping->private_data;
> >+	class = pool->size_class[class_idx];
> >+
> >+	spin_lock(&class->lock);
> >+	dec_zspage_isolation(zspage);
> >+	if (!get_zspage_isolation(zspage))
> >+		putback_zspage(class, zspage);
> >+	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,
> >+};
> >+
> >+/*
> >+ * 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)
> >+{
> >+	struct zspage *zspage, *tmp;
> >+	LIST_HEAD(free_pages);
> >+	struct zs_pool *pool = container_of(work, struct zs_pool,
> >+					free_work);
> >+
> >+	spin_lock(&pool->free_lock);
> >+	list_splice_init(&pool->free_zspage, &free_pages);
> >+	spin_unlock(&pool->free_lock);
> >+
> >+	list_for_each_entry_safe(zspage, tmp, &free_pages, list) {
> >+		list_del(&zspage->list);
> >+		lock_zspage(zspage);
> >+		__free_zspage(pool, zspage);
> >+	}
> >+};
> >+
> >  /**
> >   * zs_create_pool - Creates an allocation pool to work from.
> >   * @flags: allocation flags used to allocate pool metadata
> >@@ -1879,6 +2257,10 @@ struct zs_pool *zs_create_pool(const char *name, gfp_t flags)
> >  	if (!pool)
> >  		return NULL;
> >
> >+	INIT_WORK(&pool->free_work, async_free_zspage);
> >+	INIT_LIST_HEAD(&pool->free_zspage);
> >+	spin_lock_init(&pool->free_lock);
> >+
> >  	pool->size_class = kcalloc(zs_size_classes, sizeof(struct size_class *),
> >  			GFP_KERNEL);
> >  	if (!pool->size_class) {
> >@@ -1944,11 +2326,21 @@ struct zs_pool *zs_create_pool(const char *name, gfp_t flags)
> >  		prev_class = class;
> >  	}
> >
> >+	INIT_LIST_HEAD(&pool->free_zspage);
> >  	pool->flags = flags;
> >
> >  	if (zs_pool_stat_create(pool, name))
> >  		goto err;
> >
> >+	pool->inode = alloc_anon_inode(zsmalloc_mnt->mnt_sb);
> >+	if (IS_ERR(pool->inode)) {
> >+		pool->inode = NULL;
> >+		goto err;
> >+	}
> >+
> >+	pool->inode->i_mapping->a_ops = &zsmalloc_aops;
> >+	pool->inode->i_mapping->private_data = pool;
> >+
> >  	/*
> >  	 * Not critical, we still can use the pool
> >  	 * and user can trigger compaction manually.
> >@@ -1967,7 +2359,11 @@ void zs_destroy_pool(struct zs_pool *pool)
> >  {
> >  	int i;
> >
> >+	flush_work(&pool->free_work);
> >+
> >  	zs_unregister_shrinker(pool);
> >+	if (pool->inode)
> >+		iput(pool->inode);
> >  	zs_pool_stat_destroy(pool);
> >
> >  	for (i = 0; i < zs_size_classes; i++) {
> >@@ -1996,10 +2392,33 @@ void zs_destroy_pool(struct zs_pool *pool)
> >  }
> >  EXPORT_SYMBOL_GPL(zs_destroy_pool);
> >
> >+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 __init zs_init(void)
> >  {
> >-	int ret = zs_register_cpu_notifier();
> >+	int ret;
> >
> >+	zsmalloc_mnt = kern_mount(&zsmalloc_fs);
> >+	if (IS_ERR(zsmalloc_mnt)) {
> >+		ret = PTR_ERR(zsmalloc_mnt);
> >+		goto out;
> >+	}
> >+
> >+	ret = zs_register_cpu_notifier();
> >  	if (ret)
> >  		goto notifier_fail;
> >
> >@@ -2022,7 +2441,8 @@ static int __init zs_init(void)
> >  #endif
> >  notifier_fail:
> >  	zs_unregister_cpu_notifier();
> >-
> >+	kern_unmount(zsmalloc_mnt);
> >+out:
> >  	return ret;
> >  }
> >
> >
> 
> --
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