Re: [v8 0/4] cgroup-aware OOM killer

[Michal Hocko]

On Wed 13-09-17 14:56:07, Roman Gushchin wrote:
> On Wed, Sep 13, 2017 at 02:29:14PM +0200, Michal Hocko wrote:
[...]
> > I strongly believe that comparing only leaf memcgs
> > is more straightforward and it doesn't lead to unexpected results as
> > mentioned before (kill a small memcg which is a part of the larger
> > sub-hierarchy).
> 
> One of two main goals of this patchset is to introduce cgroup-level
> fairness: bigger cgroups should be affected more than smaller,
> despite the size of tasks inside. I believe the same principle
> should be used for cgroups.

Yes bigger cgroups should be preferred but I fail to see why bigger
hierarchies should be considered as well if they are not kill-all. And
whether non-leaf memcgs should allow kill-all is not entirely clear to
me. What would be the usecase?
Consider that it might be not your choice (as a user) how deep is your
leaf memcg. I can already see how people complain that their memcg has
been killed just because it was one level deeper in the hierarchy...

I would really start simple and only allow kill-all on leaf memcgs and
only compare leaf memcgs & root. If we ever need to kill whole
hierarchies then allow kill-all on intermediate memcgs as well and then
consider cumulative consumptions only on those that have kill-all
enabled.

Or do I miss any reasonable usecase that would suffer from such a
semantic?
-- 
Michal Hocko
SUSE Labs