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

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Date:   Wed, 13 Sep 2017 14:56:07 -0700
From:   Roman Gushchin <guro@...com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     David Rientjes <rientjes@...gle.com>, <linux-mm@...ck.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, <kernel-team@...com>,
        <cgroups@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [v8 0/4] cgroup-aware OOM killer

On Wed, Sep 13, 2017 at 02:29:14PM +0200, Michal Hocko wrote:
> On Mon 11-09-17 13:44:39, David Rientjes wrote:
> > On Mon, 11 Sep 2017, Roman Gushchin wrote:
> > 
> > > This patchset makes the OOM killer cgroup-aware.
> > > 
> > > v8:
> > >   - Do not kill tasks with OOM_SCORE_ADJ -1000
> > >   - Make the whole thing opt-in with cgroup mount option control
> > >   - Drop oom_priority for further discussions
> > 
> > Nack, we specifically require oom_priority for this to function correctly, 
> > otherwise we cannot prefer to kill from low priority leaf memcgs as 
> > required.
> 
> While I understand that your usecase might require priorities I do not
> think this part missing is a reason to nack the cgroup based selection
> and kill-all parts. This can be done on top. The only important part
> right now is the current selection semantic - only leaf memcgs vs. size
> of the hierarchy).

I agree.

> 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.

Also, the opposite will make oom_semantics more weird: it will mean
kill all tasks, but also treat memcg as a leaf cgroup.

> 
> I didn't get to read the new version of this series yet and hope to get
> to it soon.

Thanks!