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.
v2: calculate nr of objects using new.objects and new.inuse.
It is more accurate way than before.
Signed-off-by: Joonsoo Kim <iamjoonsoo....@lge.com>
diff --git a/mm/slub.c b/mm/slub.c
index ba2ca53..7204c74 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)
--
1.7.9.5
--
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