linux-kernel - Re: Android low memory killer vs. memory pressure notifications

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Message-ID: <20111220021647.GB4531@oksana.dev.rtsoft.ru>
Date:	Tue, 20 Dec 2011 06:16:47 +0400
From:	Anton Vorontsov <anton.vorontsov@...aro.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Rik van Riel <riel@...hat.com>, Pavel Machek <pavel@....cz>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	John Stultz <john.stultz@...aro.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: Android low memory killer vs. memory pressure notifications

On Mon, Dec 19, 2011 at 01:12:55PM +0100, Michal Hocko wrote:
> [Didn't get to the patch yet but a comment on memcg]
> 
> On Mon 19-12-11 06:53:28, Anton Vorontsov wrote:
> [...]
> > - Use memory controller cgroup (CGROUP_MEM_RES_CTLR) notifications from
> >   the kernel side, plus userland "manager" that would kill applications.
> > 
> >   The main downside of this approach is that mem_cg needs 20 bytes per
> >   page (on a 32 bit machine). So on a 32 bit machine with 4K pages
> >   that's approx. 0.5% of RAM, or, in other words, 5MB on a 1GB machine.
> 
> page_cgroup is 16B per page and with the current Johannes' memcg
> naturalization work (in the mmotm tree) we are down to 8B per page (we
> got rid of lru). Kamezawa has some patches to get rid of the flags so we
> will be down to 4B per page on 32b. Is this still too much?
> I would be really careful about a yet another lowmem notification
> mechanism.

4 bytes (1MB wastage on a 1GB machine) sounds much better. If there are no
other downsides of using cgroups-based low memory killer, then maybe it's
not worth doing yet another low memory notification stuff.

> >   0.5% doesn't sound too bad, but 5MB does, quite a little bit. So,
> >   mem_cg feels like an overkill for this simple task (see the driver at
> >   the very bottom).
> 
> Why is it an overkill? I think that having 2 groups (active and
> inactive) and move tasks between then sounds quite elegant.

Yep, that was the original idea. But back then mem_cg was way too costly,
so nobody seriously considered this as a solution.

Thanks,

-- 
Anton Vorontsov
Email: cbouatmailru@...il.com
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