linux-kernel - Re: [PATCH] mm, oom_adj: avoid meaningless loop to find processes sharing mm

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Message-ID: <20181009111005.GK8528@dhcp22.suse.cz>
Date:   Tue, 9 Oct 2018 13:10:05 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     ytk.lee@...sung.com, "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] mm, oom_adj: avoid meaningless loop to find processes
 sharing mm

On Tue 09-10-18 19:00:44, Tetsuo Handa wrote:
> On 2018/10/09 16:50, Michal Hocko wrote:
[...]
> >                               Well, that is unfortunate indeed and it
> > breaks the OOM_SCORE_ADJ_MIN contract. There are basically two ways here
> > 1) do not care and encourage users to use a saner way to set
> > OOM_SCORE_ADJ_MIN because doing that externally is racy anyway e.g.
> > setting it before [v]fork & exec. Btw. do we know about an actual user
> > who would care?
> 
> I'm not talking about [v]fork & exec. Why are you talking about [v]fork & exec ?

Because that is the only raceless way to set your oom_score_adj.

> > 2) add OOM_SCORE_ADJ_MIN and do not kill tasks sharing mm and do not
> > reap the mm in the rare case of the race.
> 
> That is no problem. The mistake we made in 4.6 was that we updated oom_score_adj
> to -1000 (and allowed unprivileged users to OOM-lockup the system).

I do not follow.

-- 
Michal Hocko
SUSE Labs