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Date:   Wed, 21 Aug 2019 08:47:32 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     David Rientjes <rientjes@google.com>
Cc:     Edward Chron <echron@arista.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Roman Gushchin <guro@fb.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Shakeel Butt <shakeelb@google.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, colona@arista.com
Subject: Re: [PATCH] mm/oom: Add oom_score_adj value to oom Killed process
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On Tue 20-08-19 20:25:32, David Rientjes wrote:
> On Tue, 20 Aug 2019, Edward Chron wrote:
> 
> > For an OOM event: print oom_score_adj value for the OOM Killed process to
> > document what the oom score adjust value was at the time the process was
> > OOM Killed. The adjustment value can be set by user code and it affects
> > the resulting oom_score so it is used to influence kill process selection.
> > 
> > When eligible tasks are not printed (sysctl oom_dump_tasks = 0) printing
> > this value is the only documentation of the value for the process being
> > killed. Having this value on the Killed process message documents if a
> > miscconfiguration occurred or it can confirm that the oom_score_adj
> > value applies as expected.
> > 
> > An example which illustates both misconfiguration and validation that
> > the oom_score_adj was applied as expected is:
> > 
> > Aug 14 23:00:02 testserver kernel: Out of memory: Killed process 2692
> >  (systemd-udevd) total-vm:1056800kB, anon-rss:1052760kB, file-rss:4kB,
> >  shmem-rss:0kB oom_score_adj:1000
> > 
> > The systemd-udevd is a critical system application that should have an
> > oom_score_adj of -1000. Here it was misconfigured to have a adjustment
> > of 1000 making it a highly favored OOM kill target process. The output
> > documents both the misconfiguration and the fact that the process
> > was correctly targeted by OOM due to the miconfiguration. Having
> > the oom_score_adj on the Killed message ensures that it is documented.
> > 
> > Signed-off-by: Edward Chron <echron@arista.com>
> > Acked-by: Michal Hocko <mhocko@suse.com>
> 
> Acked-by: David Rientjes <rientjes@google.com>
> 
> vm.oom_dump_tasks is pretty useful, however, so it's curious why you 
> haven't left it enabled :/

Because it generates a lot of output potentially. Think of a workload
with too many tasks which is not uncommon.
-- 
Michal Hocko
SUSE Labs