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Date:   Mon, 1 Mar 2021 13:15:02 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Yang Shi <shy828301@gmail.com>
Cc:     Johannes Weiner <hannes@cmpxchg.org>, Roman Gushchin <guro@fb.com>,
        Shakeel Butt <shakeelb@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Linux MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] doc: memcontrol: add description for oom_kill
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On Fri 26-02-21 08:42:29, Yang Shi wrote:
> On Thu, Feb 25, 2021 at 11:30 PM Michal Hocko <mhocko@suse.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.
-- 
Michal Hocko
SUSE Labs