mm: memcg: charge memcg percpu memory to the parent cgroup

mm: memcg: charge memcg percpu memory to the parent cgroup

Memory cgroups are using large chunks of percpu memory to store vmstat
data.  Yet this memory is not accounted at all, so in the case when there
are many (dying) cgroups, it's not exactly clear where all the memory is.

Because the size of memory cgroup internal structures can dramatically
exceed the size of object or page which is pinning it in the memory, it's
not a good idea to simply ignore it.  It actually breaks the isolation
between cgroups.

Let's account the consumed percpu memory to the parent cgroup.

[[email protected]: add WARN_ON_ONCE()s, per Johannes]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Roman Gushchin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Reviewed-by: Shakeel Butt <[email protected]>
Acked-by: Dennis Zhou <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Tobin C. Harding <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Waiman Long <[email protected]>
Cc: Bixuan Cui <[email protected]>
Cc: Michal Koutný <[email protected]>
Cc: Stephen Rothwell <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>