memcg: do not account memory used for cache creation

memcg: do not account memory used for cache creation

The memory we used to hold the memcg arrays is currently accounted to the
current memcg.  But that creates a problem, because that memory can only
be freed after the last user is gone.  Our only way to know which is the
last user, is to hook up to freeing time, but the fact that we still have
some in flight kmallocs will prevent freeing to happen.  I believe
therefore to be just easier to account this memory as global overhead.

Signed-off-by: Glauber Costa <glommer@openvz.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>