linux-kernel - Re: [PATCH 1/2] Add mempressure cgroup

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Date:	Wed, 9 Jan 2013 13:36:04 -0800
From:	Anton Vorontsov <anton.vorontsov@...aro.org>
To:	Glauber Costa <glommer@...allels.com>
Cc:	Tejun Heo <tj@...nel.org>, David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...e.cz>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Luiz Capitulino <lcapitulino@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Thelen <gthelen@...gle.com>,
	Leonid Moiseichuk <leonid.moiseichuk@...ia.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Minchan Kim <minchan@...nel.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	John Stultz <john.stultz@...aro.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, linaro-kernel@...ts.linaro.org,
	patches@...aro.org, kernel-team@...roid.com
Subject: Re: [PATCH 1/2] Add mempressure cgroup

On Thu, Jan 10, 2013 at 01:20:30AM +0400, Glauber Costa wrote:
[...]
> Given the above, I believe that ideally we should use this pressure
> mechanism in memcg replacing the current memcg notification mechanism.

Just a quick wonder: why would we need to place it into memcg, when we
don't need any of the memcg stuff for it? I see no benefits, not
design-wise, not implementation-wise or anything-wise. :)

We can use mempressure w/o memcg, and even then it can (or should :) be
useful (for cpuset, for example).

> More or less like timer expiration happens: you could still write
> numbers for compatibility, but those numbers would be internally mapped
> into the levels Anton is proposing, that makes *way* more sense.
> 
> If that is not possible, they should coexist as "notification" and a
> "pressure" mechanism inside memcg.
> 
> The main argument against it centered around cpusets also being able to
> participate in the play. I haven't yet understood how would it take
> place. In particular, I saw no mention to cpusets in the patches.

I didn't test it, but as I see it, once a process in a specific cpuset,
the task can only use a specific allowed zones for reclaim/alloc, i.e.
various checks like this in vmscan:

         if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
                     continue;

So, vmscan simply won't call vmpressure() if the zone is not allowed (so
we won't account that pressure, from that zone).

Thanks,
Anton
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