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Commit 0ab0abcf authored by Weijie Yang's avatar Weijie Yang Committed by Linus Torvalds
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mm/zswap: refactor the get/put routines 



The refcount routine was not fit the kernel get/put semantic exactly,
There were too many judgement statements on refcount and it could be
minus.

This patch does the following:

 - move refcount judgement to zswap_entry_put() to hide resource free function.

 - add a new function zswap_entry_find_get(), so that callers can use
   easily in the following pattern:

     zswap_entry_find_get
     .../* do something */
     zswap_entry_put

 - to eliminate compile error, move some functions declaration

This patch is based on Minchan Kim <minchan@kernel.org> 's idea and suggestion.

Signed-off-by: default avatarWeijie Yang <weijie.yang@samsung.com>
Cc: Seth Jennings <sjennings@variantweb.net>
Acked-by: default avatarMinchan Kim <minchan@kernel.org>
Cc: Bob Liu <bob.liu@oracle.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 67d13fe8

mm/zswap.c

+88 −94
Original line number Diff line number Diff line
@@ -217,6 +217,7 @@ static struct zswap_entry *zswap_entry_cache_alloc(gfp_t gfp) 
	if (!entry)

		return NULL;

	entry->refcount = 1;

	RB_CLEAR_NODE(&entry->rbnode);

	return entry;

}
@@ -225,19 +226,6 @@ static void zswap_entry_cache_free(struct zswap_entry *entry) 
	kmem_cache_free(zswap_entry_cache, entry);

}



/* caller must hold the tree lock */

static void zswap_entry_get(struct zswap_entry *entry)

{

	entry->refcount++;

}



/* caller must hold the tree lock */

static int zswap_entry_put(struct zswap_entry *entry)

{

	entry->refcount--;

	return entry->refcount;

}



/*********************************

* rbtree functions

**********************************/
@@ -285,6 +273,61 @@ static int zswap_rb_insert(struct rb_root *root, struct zswap_entry *entry, 
	return 0;

}



static void zswap_rb_erase(struct rb_root *root, struct zswap_entry *entry)

{

	if (!RB_EMPTY_NODE(&entry->rbnode)) {

		rb_erase(&entry->rbnode, root);

		RB_CLEAR_NODE(&entry->rbnode);

	}

}



/*

 * Carries out the common pattern of freeing and entry's zsmalloc allocation,

 * freeing the entry itself, and decrementing the number of stored pages.

 */

static void zswap_free_entry(struct zswap_tree *tree,

			struct zswap_entry *entry)

{

	zbud_free(tree->pool, entry->handle);

	zswap_entry_cache_free(entry);

	atomic_dec(&zswap_stored_pages);

	zswap_pool_pages = zbud_get_pool_size(tree->pool);

}



/* caller must hold the tree lock */

static void zswap_entry_get(struct zswap_entry *entry)

{

	entry->refcount++;

}



/* caller must hold the tree lock

* remove from the tree and free it, if nobody reference the entry

*/

static void zswap_entry_put(struct zswap_tree *tree,

			struct zswap_entry *entry)

{

	int refcount = --entry->refcount;



	BUG_ON(refcount < 0);

	if (refcount == 0) {

		zswap_rb_erase(&tree->rbroot, entry);

		zswap_free_entry(tree, entry);

	}

}



/* caller must hold the tree lock */

static struct zswap_entry *zswap_entry_find_get(struct rb_root *root,

				pgoff_t offset)

{

	struct zswap_entry *entry = NULL;



	entry = zswap_rb_search(root, offset);

	if (entry)

		zswap_entry_get(entry);



	return entry;

}



/*********************************

* per-cpu code

**********************************/
@@ -368,18 +411,6 @@ static bool zswap_is_full(void) 
		zswap_pool_pages);

}



/*

 * Carries out the common pattern of freeing and entry's zsmalloc allocation,

 * freeing the entry itself, and decrementing the number of stored pages.

 */

static void zswap_free_entry(struct zswap_tree *tree, struct zswap_entry *entry)

{

	zbud_free(tree->pool, entry->handle);

	zswap_entry_cache_free(entry);

	atomic_dec(&zswap_stored_pages);

	zswap_pool_pages = zbud_get_pool_size(tree->pool);

}



/*********************************

* writeback code

**********************************/
@@ -503,7 +534,7 @@ static int zswap_writeback_entry(struct zbud_pool *pool, unsigned long handle) 
	struct page *page;

	u8 *src, *dst;

	unsigned int dlen;

	int ret, refcount;

	int ret;

	struct writeback_control wbc = {

		.sync_mode = WB_SYNC_NONE,

	};
@@ -518,13 +549,12 @@ static int zswap_writeback_entry(struct zbud_pool *pool, unsigned long handle) 


	/* find and ref zswap entry */

	spin_lock(&tree->lock);

	entry = zswap_rb_search(&tree->rbroot, offset);

	entry = zswap_entry_find_get(&tree->rbroot, offset);

	if (!entry) {

		/* entry was invalidated */

		spin_unlock(&tree->lock);

		return 0;

	}

	zswap_entry_get(entry);

	spin_unlock(&tree->lock);

	BUG_ON(offset != entry->offset);
@@ -566,42 +596,35 @@ static int zswap_writeback_entry(struct zbud_pool *pool, unsigned long handle) 
	zswap_written_back_pages++;



	spin_lock(&tree->lock);



	/* drop local reference */

	zswap_entry_put(entry);

	/* drop the initial reference from entry creation */

	refcount = zswap_entry_put(entry);

	zswap_entry_put(tree, entry);



	/*

	 * There are three possible values for refcount here:

	 * (1) refcount is 1, load is in progress, unlink from rbtree,

	 *     load will free

	 * (2) refcount is 0, (normal case) entry is valid,

	 *     remove from rbtree and free entry

	 * (3) refcount is -1, invalidate happened during writeback,

	 *     free entry

	* There are two possible situations for entry here:

	* (1) refcount is 1(normal case),  entry is valid and on the tree

	* (2) refcount is 0, entry is freed and not on the tree

	*     because invalidate happened during writeback

	*  search the tree and free the entry if find entry

	*/

	if (refcount >= 0) {

		/* no invalidate yet, remove from rbtree */

		rb_erase(&entry->rbnode, &tree->rbroot);

	}

	if (entry == zswap_rb_search(&tree->rbroot, offset))

		zswap_entry_put(tree, entry);

	spin_unlock(&tree->lock);

	if (refcount <= 0) {

		/* free the entry */

		zswap_free_entry(tree, entry);

		return 0;

	}

	return -EAGAIN;



	goto end;



	/*

	* if we get here due to ZSWAP_SWAPCACHE_EXIST

	* a load may happening concurrently

	* it is safe and okay to not free the entry

	* if we free the entry in the following put

	* it it either okay to return !0

	*/

fail:

	spin_lock(&tree->lock);

	refcount = zswap_entry_put(entry);

	if (refcount <= 0) {

		/* invalidate happened, consider writeback as success */

		zswap_free_entry(tree, entry);

		ret = 0;

	}

	zswap_entry_put(tree, entry);

	spin_unlock(&tree->lock);



end:

	return ret;

}
@@ -685,11 +708,8 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, 
		if (ret == -EEXIST) {

			zswap_duplicate_entry++;

			/* remove from rbtree */

			rb_erase(&dupentry->rbnode, &tree->rbroot);

			if (!zswap_entry_put(dupentry)) {

				/* free */

				zswap_free_entry(tree, dupentry);

			}

			zswap_rb_erase(&tree->rbroot, dupentry);

			zswap_entry_put(tree, dupentry);

		}

	} while (ret == -EEXIST);

	spin_unlock(&tree->lock);
@@ -718,17 +738,16 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset, 
	struct zswap_entry *entry;

	u8 *src, *dst;

	unsigned int dlen;

	int refcount, ret;

	int ret;



	/* find */

	spin_lock(&tree->lock);

	entry = zswap_rb_search(&tree->rbroot, offset);

	entry = zswap_entry_find_get(&tree->rbroot, offset);

	if (!entry) {

		/* entry was written back */

		spin_unlock(&tree->lock);

		return -1;

	}

	zswap_entry_get(entry);

	spin_unlock(&tree->lock);



	/* decompress */
@@ -743,22 +762,9 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset, 
	BUG_ON(ret);



	spin_lock(&tree->lock);

	refcount = zswap_entry_put(entry);

	if (likely(refcount)) {

		spin_unlock(&tree->lock);

		return 0;

	}

	zswap_entry_put(tree, entry);

	spin_unlock(&tree->lock);



	/*

	 * We don't have to unlink from the rbtree because

	 * zswap_writeback_entry() or zswap_frontswap_invalidate page()

	 * has already done this for us if we are the last reference.

	 */

	/* free */



	zswap_free_entry(tree, entry);



	return 0;

}
@@ -767,7 +773,6 @@ static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offset) 
{

	struct zswap_tree *tree = zswap_trees[type];

	struct zswap_entry *entry;

	int refcount;



	/* find */

	spin_lock(&tree->lock);
@@ -779,20 +784,12 @@ static void zswap_frontswap_invalidate_page(unsigned type, pgoff_t offset) 
	}



	/* remove from rbtree */

	rb_erase(&entry->rbnode, &tree->rbroot);

	zswap_rb_erase(&tree->rbroot, entry);



	/* drop the initial reference from entry creation */

	refcount = zswap_entry_put(entry);

	zswap_entry_put(tree, entry);



	spin_unlock(&tree->lock);



	if (refcount) {

		/* writeback in progress, writeback will free */

		return;

	}



	/* free */

	zswap_free_entry(tree, entry);

}



/* frees all zswap entries for the given swap type */
@@ -806,11 +803,8 @@ static void zswap_frontswap_invalidate_area(unsigned type) 


	/* walk the tree and free everything */

	spin_lock(&tree->lock);

	rbtree_postorder_for_each_entry_safe(entry, n, &tree->rbroot, rbnode) {

		zbud_free(tree->pool, entry->handle);

		zswap_entry_cache_free(entry);

		atomic_dec(&zswap_stored_pages);

	}

	rbtree_postorder_for_each_entry_safe(entry, n, &tree->rbroot, rbnode)

		zswap_free_entry(tree, entry);

	tree->rbroot = RB_ROOT;

	spin_unlock(&tree->lock);