linux-kernel - Re: [RFC PATCH] memcg: oom: fix totalpages calculation for swappiness==0

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Date:	Thu, 11 Oct 2012 10:50:38 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	David Rientjes <rientjes@...gle.com>
Cc:	linux-mm@...ck.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] memcg: oom: fix totalpages calculation for
 swappiness==0

On Wed 10-10-12 13:50:21, David Rientjes wrote:
> On Wed, 10 Oct 2012, Michal Hocko wrote:
> 
> > Hi,
> > I am sending the patch below as an RFC because I am not entirely happy
> > about myself and maybe somebody can come up with a different approach
> > which would be less hackish.
> 
> I don't see this as hackish, 

I didn't like how swappiness spreads outside of the LRU scanning code...

> if memory.swappiness limits access to swap then this shouldn't be
> factored into the calculation, and that's what your patch fixes.
> 
> The reason why the process with the largest rss isn't killed in this case 
> is because all processes have CAP_SYS_ADMIN so they get a 3% bonus;

OK I should have mentioned that I have tested it as root which makes a
big difference with the current upstream as totalpages are considered
only if adj!=0. 
I have originally seen the problem in 3.0 kernel (with fe35004f applied)
where the calculation is different (missing a7f638f9) and we always
consider total_pages there so it doesn't depend on root or oom_score_adj.

> when factoring swap into the calculation and subtracting 3% from
> the score in oom_badness(), they all end up having an internal
> score of 1 so they are all considered equal.  It appears like the
> cgroup_iter_next() iteration for memcg ooms does this in reverse
> order, which is actually helpful so it will select the task that is
> newer.
> 
> The only suggestion I have to make is specify this is for 
> memory.swappiness in the patch title, otherwise:

OK. I will also update the changelog to mention oom_score_adj and
CAP_SYS_ADMIN, mark the patch for stable and repost it.

> Acked-by: David Rientjes <rientjes@...gle.com>

Thanks
-- 
Michal Hocko
SUSE Labs
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