[PATCH v11 01/15] memcg: make cache index determination more robust

From: Vladimir Davydov
Date: Thu Oct 24 2013 - 08:05:25 EST

From: Glauber Costa <glommer@xxxxxxxxxx>

I caught myself doing something like the following outside memcg core:

memcg_id = -1;
if (memcg && memcg_kmem_is_active(memcg))
memcg_id = memcg_cache_id(memcg);

to be able to handle all possible memcgs in a sane manner. In particular, the
root cache will have kmemcg_id = -1 (just because we don't call memcg_kmem_init
to the root cache since it is not limitable). We have always coped with that by
making sure we sanitize which cache is passed to memcg_cache_id. Although this
example is given for root, what we really need to know is whether or not a
cache is kmem active.

But outside the memcg core testing for root, for instance, is not trivial since
we don't export mem_cgroup_is_root. I ended up realizing that this tests really
belong inside memcg_cache_id. This patch moves a similar but stronger test
inside memcg_cache_id and make sure it always return a meaningful value.

Signed-off-by: Glauber Costa <glommer@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
mm/memcontrol.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 34d3ca9..0712277 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3057,7 +3057,9 @@ void memcg_cache_list_add(struct mem_cgroup *memcg, struct kmem_cache *cachep)
int memcg_cache_id(struct mem_cgroup *memcg)
- return memcg ? memcg->kmemcg_id : -1;
+ if (!memcg || !memcg_can_account_kmem(memcg))
+ return -1;
+ return memcg->kmemcg_id;


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