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authorVladimir Davydov <vdavydov@virtuozzo.com>2016-03-17 14:17:29 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-03-17 15:09:34 -0700
commitfcff7d7eebe6d31e2ce20d994555c86a90197034 (patch)
tree776a49bee21274e04baf973a281fb764df4764b1 /mm/memcontrol.c
parent6a618957ad17d8f4f4c7eeede752685374b1b176 (diff)
mm: memcontrol: do not bypass slab charge if memcg is offline
Slab pages are charged in two steps. First, an appropriate per memcg cache is selected (see memcg_kmem_get_cache) basing on the current context, then the new slab page is charged to the memory cgroup which the selected cache was created for (see memcg_charge_slab -> __memcg_kmem_charge_memcg). It is OK to bypass kmemcg charge at step 1, but if step 1 succeeded and we successfully allocated a new slab page, step 2 must be performed, otherwise we would get a per memcg kmem cache which contains a slab that does not hold a reference to the memory cgroup owning the cache. Since per memcg kmem caches are destroyed on memcg css free, this could result in freeing a cache while there are still active objects in it. However, currently we will bypass slab page charge if the memory cgroup owning the cache is offline (see __memcg_kmem_charge_memcg). This is very unlikely to occur in practice, because for this to happen a process must be migrated to a different cgroup and the old cgroup must be removed while the process is in kmalloc somewhere between steps 1 and 2 (e.g. trying to allocate a new page). Nevertheless, it's still better to eliminate such a possibility. Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/memcontrol.c')
-rw-r--r--mm/memcontrol.c8
1 files changed, 3 insertions, 5 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 42882c1e7fce..5c9d45e4c739 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2325,9 +2325,6 @@ int __memcg_kmem_charge_memcg(struct page *page, gfp_t gfp, int order,
struct page_counter *counter;
int ret;
- if (!memcg_kmem_online(memcg))
- return 0;
-
ret = try_charge(memcg, gfp, nr_pages);
if (ret)
return ret;
@@ -2346,10 +2343,11 @@ int __memcg_kmem_charge_memcg(struct page *page, gfp_t gfp, int order,
int __memcg_kmem_charge(struct page *page, gfp_t gfp, int order)
{
struct mem_cgroup *memcg;
- int ret;
+ int ret = 0;
memcg = get_mem_cgroup_from_mm(current->mm);
- ret = __memcg_kmem_charge_memcg(page, gfp, order, memcg);
+ if (memcg_kmem_online(memcg))
+ ret = __memcg_kmem_charge_memcg(page, gfp, order, memcg);
css_put(&memcg->css);
return ret;
}