kmemcg: don't allocate extra memory for root memcg_cache_params

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

Signed-off-by: Andrey Vagin <avagin@openvz.org>
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3b83957..5ca1dcf 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3121,7 +3121,7 @@ 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) {
@@ -3164,13 +3164,16 @@ 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)