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

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Message-ID: <CAHbLzkpvWJn3dOrLLPvtyKY6qEs5Nv57rc7K+_+eL35eCDnywg@mail.gmail.com>
Date:   Mon, 1 Mar 2021 09:07:03 -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 Mon, Mar 1, 2021 at 4:15 AM Michal Hocko <mhocko@...e.com> wrote:
>
> On Fri 26-02-21 08:42:29, Yang Shi wrote:
> > 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.
>
> I believe the reson is that v1 can have tasks in the intermediate
> (non-leaf) memcgs. So you wouldn't have a way to tell whether the oom
> kill has happened in such a memcg or somewhere down the hierarchy.

Aha, I forgot it, that's bad. Although we don't have tasks in
intermediate nodes in practice, I do understand it is not forbidden as
cgroup v2.

> --
> Michal Hocko
> SUSE Labs