linux-kernel - Re: [patch -mm v2 2/3] mm, memcg: replace cgroup aware oom killer mount option with tunable

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Message-ID: <20180130121315.GA5888@castle.DHCP.thefacebook.com>
Date:   Tue, 30 Jan 2018 12:13:22 +0000
From:   Roman Gushchin <guro@...com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     Tejun Heo <tj@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        <kernel-team@...com>, <cgroups@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-mm@...ck.org>
Subject: Re: [patch -mm v2 2/3] mm, memcg: replace cgroup aware oom killer
 mount option with tunable

On Tue, Jan 30, 2018 at 01:08:52PM +0100, Michal Hocko wrote:
> On Tue 30-01-18 11:58:51, Roman Gushchin wrote:
> > On Tue, Jan 30, 2018 at 09:54:45AM +0100, Michal Hocko wrote:
> > > On Mon 29-01-18 11:11:39, Tejun Heo wrote:
> > 
> > Hello, Michal!
> > 
> > > diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
> > > index 2eaed1e2243d..67bdf19f8e5b 100644
> > > --- a/Documentation/cgroup-v2.txt
> > > +++ b/Documentation/cgroup-v2.txt
> > > @@ -1291,8 +1291,14 @@ This affects both system- and cgroup-wide OOMs. For a cgroup-wide OOM
> > >  the memory controller considers only cgroups belonging to the sub-tree
> > >  of the OOM'ing cgroup.
> > >  
> > > -The root cgroup is treated as a leaf memory cgroup, so it's compared
> > > -with other leaf memory cgroups and cgroups with oom_group option set.
> >                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > IMO, this statement is important. Isn't it?
> > 
> > > +Leaf cgroups are compared based on their cumulative memory usage. The
> > > +root cgroup is treated as a leaf memory cgroup as well, so it's
> > > +compared with other leaf memory cgroups. Due to internal implementation
> > > +restrictions the size of the root cgroup is a cumulative sum of
> > > +oom_badness of all its tasks (in other words oom_score_adj of each task
> > > +is obeyed). Relying on oom_score_adj (appart from OOM_SCORE_ADJ_MIN)
> > > +can lead to overestimating of the root cgroup consumption and it is
> > 
> > Hm, and underestimating too. Also OOM_SCORE_ADJ_MIN isn't any different
> > in this case. Say, all tasks except a small one have OOM_SCORE_ADJ set to
> > -999, this means the root croup has extremely low chances to be elected.
> > 
> > > +therefore discouraged. This might change in the future, though.
> > 
> > Other than that looks very good to me.
> 
> This?
> 
> diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
> index 2eaed1e2243d..34ad80ee90f2 100644
> --- a/Documentation/cgroup-v2.txt
> +++ b/Documentation/cgroup-v2.txt
> @@ -1291,8 +1291,15 @@ This affects both system- and cgroup-wide OOMs. For a cgroup-wide OOM
>  the memory controller considers only cgroups belonging to the sub-tree
>  of the OOM'ing cgroup.
>  
> -The root cgroup is treated as a leaf memory cgroup, so it's compared
> -with other leaf memory cgroups and cgroups with oom_group option set.
> +Leaf cgroups and cgroups with oom_group option set are compared based
> +on their cumulative memory usage. The root cgroup is treated as a
> +leaf memory cgroup as well, so it's compared with other leaf memory
> +cgroups. Due to internal implementation restrictions the size of
> +the root cgroup is a cumulative sum of oom_badness of all its tasks
> +(in other words oom_score_adj of each task is obeyed). Relying on
> +oom_score_adj (appart from OOM_SCORE_ADJ_MIN) can lead to over or
> +underestimating of the root cgroup consumption and it is therefore
> +discouraged. This might change in the future, though.

Acked-by: Roman Gushchin <guro@...com>

Thank you!