On Tue 02-10-12 13:15:43, Glauber Costa wrote:

On 10/01/2012 09:00 PM, Michal Hocko wrote:

quoted

On Tue 25-09-12 12:52:50, Glauber Costa wrote:

quoted

quoted

For the root memcg, there is no need to rely on the res_counters.

This is true only if there are no children groups but once there is at
least one we have to move global statistics into root res_counter and
start using it since then. This is a tricky part because it has to be
done atomically so that we do not miss anything.

Why can't we shortcut it all the time?

Because it has its own tasks and we are still not at use_hierarchy := 1

It makes a lot of sense to use the root cgroup as the sum of everything,
IOW, global counters. Otherwise you are left in a situation where you
had global statistics, and all of a sudden, when a group is created, you
start having just a subset of that, excluding the tasks in root.

Yes because if there are no other tasks then, well, global == root. Once
you have more groups (with tasks of course) then it depends on our
favorite use_hierarchy buddy.

If we can always assume root will have the sum of *all* tasks, including
the ones in root, we should never need to rely on root res_counters.

but we are not there yet.

-- 
Michal Hocko
SUSE Labs