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>

1 files changed, 9 insertions, 8 deletions

diff --git a/mm/slub.c b/mm/slub.c
index aa0728daf8bb..8f73593d4f21 100644
--- 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)