linux-kernel - Re: [PATCH v2] mm: oom: deduplicate victim selection code for memcg and global oom

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Date:	Fri, 1 Jul 2016 13:18:36 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Vladimir Davydov <vdavydov@...tuozzo.com>
Cc:	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm: oom: deduplicate victim selection code for memcg
 and global oom

On Tue 28-06-16 19:16:42, Vladimir Davydov wrote:
> On Mon, Jun 27, 2016 at 05:14:31PM -0700, David Rientjes wrote:
> > On Mon, 27 Jun 2016, Vladimir Davydov wrote:
> > 
> > > When selecting an oom victim, we use the same heuristic for both memory
> > > cgroup and global oom. The only difference is the scope of tasks to
> > > select the victim from. So we could just export an iterator over all
> > > memcg tasks and keep all oom related logic in oom_kill.c, but instead we
> > > duplicate pieces of it in memcontrol.c reusing some initially private
> > > functions of oom_kill.c in order to not duplicate all of it. That looks
> > > ugly and error prone, because any modification of select_bad_process
> > > should also be propagated to mem_cgroup_out_of_memory.
> > > 
> > > Let's rework this as follows: keep all oom heuristic related code
> > > private to oom_kill.c and make oom_kill.c use exported memcg functions
> > > when it's really necessary (like in case of iterating over memcg tasks).
> > > 
> > 
> > I don't know how others feel, but this actually turns out harder to read 
> > for me with all the extra redirection with minimal savings (a few dozen 
> > lines of code).
> 
> Well, if you guys find the code difficult to read after this patch,
> let's leave it as is. Sorry for the noise.

I didn't get to read the patch yet and will be offline for next few
days. I will have a look later. I believe that this is an area which is
worth cleaning up and get rid of duplication. Whether your approach is
right one I cannot tell right now. I found the previous version harder
to read than a simpler approach I have posted. Anyway I will have a look
later. And this is definitelly not a noise...
-- 
Michal Hocko
SUSE Labs