linux-kernel - Re: [patch] mm, oom: make a last minute check to prevent unnecessary memcg oom kills

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Message-ID: <20200318095710.GG21362@dhcp22.suse.cz>
Date:   Wed, 18 Mar 2020 10:57:10 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Ami Fischman <fischman@...gle.com>
Cc:     Robert Kolchmeyer <rkolchmeyer@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [patch] mm, oom: make a last minute check to prevent unnecessary
 memcg oom kills

On Tue 17-03-20 12:00:45, Ami Fischman wrote:
> On Tue, Mar 17, 2020 at 11:26 AM Robert Kolchmeyer
> <rkolchmeyer@...gle.com> wrote:
> >
> > On Tue, Mar 10, 2020 at 3:54 PM David Rientjes <rientjes@...gle.com> wrote:
> > >
> > > Robert, could you elaborate on the user-visible effects of this issue that
> > > caused it to initially get reported?
> >
> > Ami (now cc'ed) knows more, but here is my understanding.
> 
> Robert's description of the mechanics we observed is accurate.
> 
> We discovered this regression in the oom-killer's behavior when
> attempting to upgrade our system. The fraction of the system that
> went unhealthy due to this issue was approximately equal to the
> _sum_ of all other causes of unhealth, which are many and varied,
> but each of which contribute only a small amount of
> unhealth. This issue forced a rollback to the previous kernel
> where we ~never see this behavior, returning our unhealth levels
> to the previous background levels.

Could you be more specific on the good vs. bad kernel versions? Because
I do not remember any oom changes that would affect the
time-to-check-time-to-kill race. The timing might be slightly different
in each kernel version of course.

-- 
Michal Hocko
SUSE Labs