linux-kernel - Re: OOM: Better, but still there on

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Date:   Sat, 17 Dec 2016 23:44:45 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Nils Holland <nholland@...ys.org>, Michal Hocko <mhocko@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Chris Mason <clm@...com>, David Sterba <dsterba@...e.cz>,
        linux-btrfs@...r.kernel.org
Subject: Re: OOM: Better, but still there on

On 2016/12/17 21:59, Nils Holland wrote:
> On Sat, Dec 17, 2016 at 01:02:03AM +0100, Michal Hocko wrote:
>> mount -t tracefs none /debug/trace
>> echo 1 > /debug/trace/events/vmscan/enable
>> cat /debug/trace/trace_pipe > trace.log
>>
>> should help
>> [...]
> 
> No problem! I enabled writing the trace data to a file and then tried
> to trigger another OOM situation. That worked, this time without a
> complete kernel panic, but with only my processes being killed and the
> system becoming unresponsive. When that happened, I let it run for
> another minute or two so that in case it was still logging something
> to the trace file, it could continue to do so some time longer. Then I
> rebooted with the only thing that still worked, i.e. by means of magic
> SysRequest.

Under OOM situation, writing to a file on disk unlikely works. Maybe
logging via network ( "cat /debug/trace/trace_pipe > /dev/udp/$ip/$port"
if your are using bash) works better. (I wish we can do it from kernel
so that /bin/cat is not disturbed by delays due to page fault.)

If you can configure netconsole for logging OOM killer messages and
UDP socket for logging trace_pipe messages, udplogger at
https://osdn.net/projects/akari/scm/svn/tree/head/branches/udplogger/
might fit for logging both output with timestamp into a single file.