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: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Acked-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

diff --git a/mm/slub.c b/mm/slub.c
index aa0728daf8bb37c503c6518b7dd1ec414fdaef80..8f73593d4f21015ab38fef48f85744691e8b4492 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -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)