memcg: fast hierarchy-aware child test
authorGlauber Costa <glommer@parallels.com>
Sat, 23 Feb 2013 00:34:53 +0000 (16:34 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Sun, 24 Feb 2013 01:50:18 +0000 (17:50 -0800)
commitb5f99b537d047072bd50ff5c51000613eb537be8
tree59d1cae2ef46ede8f966226782661fbe8da5825b
parentd142e3e66731a0fb205a8158f5eec6f79a2ee478
memcg: fast hierarchy-aware child test

Currently, we use cgroups' provided list of children to verify if it is
safe to proceed with any value change that is dependent on the cgroup
being empty.

This is less than ideal, because it enforces a dependency over cgroup
core that we would be better off without.  The solution proposed here is
to iterate over the child cgroups and if any is found that is already
online, we bounce and return: we don't really care how many children we
have, only if we have any.

This is also made to be hierarchy aware.  IOW, cgroups with hierarchy
disabled, while they still exist, will be considered for the purpose of
this interface as having no children.

[akpm@linux-foundation.org: tweak comments]
Signed-off-by: Glauber Costa <glommer@parallels.com>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Hiroyuki Kamezawa <kamezawa.hiroyuki@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/memcontrol.c