linux-kernel - Re: [PATCH 1/5] mm, oom: introduce oom reaper

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Message-ID: <20160215205028.GE9223@dhcp22.suse.cz>
Date:	Mon, 15 Feb 2016 21:50:29 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	akpm@...ux-foundation.org, rientjes@...gle.com, mgorman@...e.de,
	oleg@...hat.com, torvalds@...ux-foundation.org, hughd@...gle.com,
	andrea@...nel.org, riel@...hat.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] mm, oom: introduce oom reaper

On Sat 06-02-16 22:22:20, Tetsuo Handa wrote:
> Michal Hocko wrote:
> > There is one notable exception to this, though, if the OOM victim was
> > in the process of coredumping the result would be incomplete. This is
> > considered a reasonable constrain because the overall system health is
> > more important than debugability of a particular application.
> 
> Is it possible to clarify what "the result would be incomplete" mean?
> 
>   (1) The size of coredump file becomes smaller than it should be, and
>       data in reaped pages is not included into the file.
> 
>   (2) The size of coredump file does not change, and data in reaped pages
>       is included into the file as NUL byte.

AFAIU this will be the case. We are not destroying VMAs we are just
unmapping the page ranges. So what would happen is that the core dump
will contain zero pages for anonymous mappings. This might change in
future though because the oom repear might be extended to do more work
(e.g. drop associated page tables when I would expect the core dumping
could SEGV).

-- 
Michal Hocko
SUSE Labs