linux-kernel - Re: [PATCH 1/6] mm, oom: do not loop over all tasks if there are no external tasks sharing mm

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Message-ID: <20160527071507.GC27686@dhcp22.suse.cz>
Date:	Fri, 27 May 2016 09:15:08 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:	linux-mm@...ck.org, rientjes@...gle.com, oleg@...hat.com,
	vdavydov@...allels.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] mm, oom: do not loop over all tasks if there are no
 external tasks sharing mm

On Fri 27-05-16 08:45:10, Michal Hocko wrote:
[...]
> It is still an operation which is not needed for 99% of situations. So
> if we do not need it for correctness then I do not think this is worth
> bothering.

Since you have pointed out exit_mm vs. __exit_signal race yesterday I
was thinking how to make the check reliable. Even
atomic_read(mm->mm_users) > get_nr_threads() is not reliable and we can
miss other tasks just because the current thread group is mostly past
exit_mm. So far I couldn't find a way to tweak this around though.
I will think about it more but I am afraid that a flag would be really
needed afterall.
-- 
Michal Hocko
SUSE Labs