linux-kernel - Re: [patch 4/8] memcg: rework soft limit reclaim

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Date:	Thu, 16 Jun 2011 13:41:56 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Ying Han <yinghan@...gle.com>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>, Greg Thelen <gthelen@...gle.com>,
	Michel Lespinasse <walken@...gle.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [patch 4/8] memcg: rework soft limit reclaim

On Wed 15-06-11 15:48:25, Ying Han wrote:
> On Thu, Jun 9, 2011 at 8:00 AM, Michal Hocko <mhocko@...e.cz> wrote:
> > On Thu 02-06-11 22:25:29, Ying Han wrote:
[...]
> > yes, this makes sense but I am not sure about the right(tm) value of the
> > MEMCG_SOFTLIMIT_RECLAIM_PRIORITY. 2 sounds too low. You would do quite a
> > lot of loops
> > (DEFAULT_PRIORITY-MEMCG_SOFTLIMIT_RECLAIM_PRIORITY) * zones * memcg_count
> > without any progress (assuming that all of them are under soft limit
> > which doesn't sound like a totally artificial configuration) until you
> > allow reclaiming from groups that are under soft limit. Then, when you
> > finally get to reclaiming, you scan rather aggressively.
> 
> Fair enough, something smarter is definitely needed :)
> 
> >
> > Maybe something like 3/4 of DEFAULT_PRIORITY? You would get 3 times
> > over all (unbalanced) zones and all cgroups that are above the limit
> > (scanning max{1/4096+1/2048+1/1024, 3*SWAP_CLUSTER_MAX} of the LRUs for
> > each cgroup) which could be enough to collect the low hanging fruit.
> 
> Hmm, that sounds more reasonable than the initial proposal.
> 
> For the same worst case where all the memcgs are blow their soft
> limit, we need to scan 3 times of total memcgs before actually doing

it is not scanning what we do. We just walk through all existing memcgs.
I think that the real issue here is how much we scan when we start
doing something useful. Maybe even DEFAULT_PRIORITY-3 is too much as
well. dunno.
-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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