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

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?

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.

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.

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