Commit 633b0764 authored by Joonsoo Kim's avatar Joonsoo Kim Committed by Pekka Enberg
Browse files

slub: correct to calculate num of acquired objects in get_partial_node() 



There is a subtle bug when calculating a number of acquired objects.

Currently, we calculate "available = page->objects - page->inuse",
after acquire_slab() is called in get_partial_node().

In acquire_slab() with mode = 1, we always set new.inuse = page->objects.
So,

	acquire_slab(s, n, page, object == NULL);

	if (!object) {
		c->page = page;
		stat(s, ALLOC_FROM_PARTIAL);
		object = t;
		available = page->objects - page->inuse;

		!!! availabe is always 0 !!!
	...

Therfore, "available > s->cpu_partial / 2" is always false and
we always go to second iteration.
This patch correct this problem.

After that, we don't need return value of put_cpu_partial().
So remove it.

Reviewed-by: default avatarWanpeng Li <liwanp@linux.vnet.ibm.com>
Acked-by: default avatarChristoph Lameter <cl@linux.com>
Signed-off-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: default avatarPekka Enberg <penberg@kernel.org>
parent 7d557b3c

mm/slub.c

+9 −8
Original line number Diff line number Diff line
@@ -1493,7 +1493,7 @@ static inline void remove_partial(struct kmem_cache_node *n, 
 */

static inline void *acquire_slab(struct kmem_cache *s,

		struct kmem_cache_node *n, struct page *page,

		int mode)

		int mode, int *objects)

{

	void *freelist;

	unsigned long counters;
@@ -1507,6 +1507,7 @@ static inline void *acquire_slab(struct kmem_cache *s, 
	freelist = page->freelist;

	counters = page->counters;

	new.counters = counters;

	*objects = new.objects - new.inuse;

	if (mode) {

		new.inuse = page->objects;

		new.freelist = NULL;
@@ -1528,7 +1529,7 @@ static inline void *acquire_slab(struct kmem_cache *s, 
	return freelist;

}



static int put_cpu_partial(struct kmem_cache *s, struct page *page, int drain);

static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain);

static inline bool pfmemalloc_match(struct page *page, gfp_t gfpflags);



/*
@@ -1539,6 +1540,8 @@ static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n, 
{

	struct page *page, *page2;

	void *object = NULL;

	int available = 0;

	int objects;



	/*

	 * Racy check. If we mistakenly see no partial slabs then we
@@ -1552,22 +1555,21 @@ static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n, 
	spin_lock(&n->list_lock);

	list_for_each_entry_safe(page, page2, &n->partial, lru) {

		void *t;

		int available;



		if (!pfmemalloc_match(page, flags))

			continue;



		t = acquire_slab(s, n, page, object == NULL);

		t = acquire_slab(s, n, page, object == NULL, &objects);

		if (!t)

			break;



		available += objects;

		if (!object) {

			c->page = page;

			stat(s, ALLOC_FROM_PARTIAL);

			object = t;

			available =  page->objects - page->inuse;

		} else {

			available = put_cpu_partial(s, page, 0);

			put_cpu_partial(s, page, 0);

			stat(s, CPU_PARTIAL_NODE);

		}

		if (kmem_cache_debug(s) || available > s->cpu_partial / 2)
@@ -1946,7 +1948,7 @@ static void unfreeze_partials(struct kmem_cache *s, 
 * If we did not find a slot then simply move all the partials to the

 * per node partial list.

 */

static int put_cpu_partial(struct kmem_cache *s, struct page *page, int drain)

static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain)

{

	struct page *oldpage;

	int pages;
@@ -1984,7 +1986,6 @@ static int put_cpu_partial(struct kmem_cache *s, struct page *page, int drain) 
		page->next = oldpage;



	} while (this_cpu_cmpxchg(s->cpu_slab->partial, oldpage, page) != oldpage);

	return pobjects;

}



static inline void flush_slab(struct kmem_cache *s, struct kmem_cache_cpu *c)

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