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: <20160527064510.GA27686@dhcp22.suse.cz>
Date:	Fri, 27 May 2016 08:45:10 +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 01:14:35, Tetsuo Handa wrote:
> 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.

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.

-- 
Michal Hocko
SUSE Labs