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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Date:	Fri, 27 May 2016 01:14:35 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	mhocko@...nel.org
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

Michal Hocko wrote:
> On Fri 27-05-16 00:25:23, Tetsuo Handa wrote:
> > I think that remembering whether this mm might be shared between
> > multiple thread groups at clone() time (i.e. whether
> > clone(CLONE_VM without CLONE_SIGHAND) was ever requested on this mm)
> > is safe (given that that thread already got SIGKILL or is exiting).
> 
> I was already playing with that idea but I didn't want to add anything
> to the fork path which is really hot. This patch is not really needed
> for the rest. It just felt like a nice optimization. I do not think it
> is worth deeper changes in the fast paths.

"[PATCH 6/6] mm, oom: fortify task_will_free_mem" depends on [PATCH 1/6].
You will need to update [PATCH 6/6].

It seems to me that [PATCH 6/6] resembles
http://lkml.kernel.org/r/201605250005.GHH26082.JOtQOSLMFFOFVH@I-love.SAKURA.ne.jp .
I think we will be happy if we can speed up mm_is_reapable() test using
"whether this mm might be shared between multiple thread groups" flag.
I don't think updating such flag at clone() is too heavy operation to add.