linux-kernel - Re: [PATCH] doc: memcontrol: add description for oom

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Date:   Fri, 26 Feb 2021 08:42:29 -0800
From:   Yang Shi <shy828301@...il.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Johannes Weiner <hannes@...xchg.org>, Roman Gushchin <guro@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] doc: memcontrol: add description for oom_kill

On Thu, Feb 25, 2021 at 11:30 PM Michal Hocko <mhocko@...e.com> wrote:
>
> On Thu 25-02-21 18:12:54, Yang Shi wrote:
> > When debugging an oom issue, I found the oom_kill counter of memcg is
> > confusing.  At the first glance without checking document, I thought it
> > just counts for memcg oom, but it turns out it counts both global and
> > memcg oom.
>
> Yes, this is the case indeed. The point of the counter was to count oom
> victims from the memcg rather than matching that to the source of the
> oom. Rememeber that this could have been a memcg oom up in the
> hierarchy as well. Counting victims on the oom origin could be equally

Yes, it is updated hierarchically on v2, but not on v1. I'm supposed
this is because v1 may work in non-hierarchcal mode? If this is the
only reason we may be able to remove this to get aligned with v2 since
non-hierarchal mode is no longer supported.

> confusing because in many cases there would be no victim counted for the
> above mentioned memcg ooms.
>
> > The cgroup v2 documents it, but the description is missed for cgroup v1.
> >
> > Signed-off-by: Yang Shi <shy828301@...il.com>
>
> Acked-by: Michal Hocko <mhocko@...e.com>
>
> > ---
> >  Documentation/admin-guide/cgroup-v1/memory.rst | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/Documentation/admin-guide/cgroup-v1/memory.rst b/Documentation/admin-guide/cgroup-v1/memory.rst
> > index 0936412e044e..44d5429636e2 100644
> > --- a/Documentation/admin-guide/cgroup-v1/memory.rst
> > +++ b/Documentation/admin-guide/cgroup-v1/memory.rst
> > @@ -851,6 +851,9 @@ At reading, current status of OOM is shown.
> >         (if 1, oom-killer is disabled)
> >       - under_oom        0 or 1
> >         (if 1, the memory cgroup is under OOM, tasks may be stopped.)
> > +        - oom_kill         integer counter
> > +          The number of processes belonging to this cgroup killed by any
> > +          kind of OOM killer.
> >
> >  11. Memory Pressure
> >  ===================
> > --
> > 2.26.2
> >
>
> --
> Michal Hocko
> SUSE Labs