[Devel] Re: [RFC 1/4] memcg: provide root figures from system totals

[Glauber Costa]

On 10/01/2012 09:00 PM, Michal Hocko wrote:
> On Tue 25-09-12 12:52:50, Glauber Costa wrote:
>> > 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.