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Subject[PATCH] kmemcg: don't allocate extra memory for root memcg_cache_params (v2)
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The memcg_cache_params structure contains the common part and the union,
which represents two different types of data: one for root cashes and
another for child caches.

The size of child data is fixed. The size of the memcg_caches array is
calculated in runtime.

Currently the size of memcg_cache_params for root caches is calculated
incorrectly, because it includes the size of parameters for child caches.

ssize_t size = memcg_caches_array_size(num_groups);
size *= sizeof(void *);

size += sizeof(struct memcg_cache_params);

v2: Fix a typo in calculations

Cc: Glauber Costa <glommer@openvz.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrey Vagin <avagin@openvz.org>
---
mm/memcontrol.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index c5792a5..2e47fea 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3140,7 +3140,7 @@ int memcg_update_cache_size(struct kmem_cache *s, int num_groups)
ssize_t size = memcg_caches_array_size(num_groups);

size *= sizeof(void *);
- size += sizeof(struct memcg_cache_params);
+ size += offsetof(struct memcg_cache_params, memcg_caches);

s->memcg_params = kzalloc(size, GFP_KERNEL);
if (!s->memcg_params) {
@@ -3183,13 +3183,16 @@ int memcg_update_cache_size(struct kmem_cache *s, int num_groups)
int memcg_register_cache(struct mem_cgroup *memcg, struct kmem_cache *s,
struct kmem_cache *root_cache)
{
- size_t size = sizeof(struct memcg_cache_params);
+ size_t size;

if (!memcg_kmem_enabled())
return 0;

- if (!memcg)
+ if (!memcg) {
+ size = offsetof(struct memcg_cache_params, memcg_caches);
size += memcg_limited_groups_array_size * sizeof(void *);
+ } else
+ size = sizeof(struct memcg_cache_params);

s->memcg_params = kzalloc(size, GFP_KERNEL);
if (!s->memcg_params)
--
1.8.3.1


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