linux-kernel - Re: [patch v3 -mm 3/3] vmscan, memcg: Do softlimit reclaim also for targeted reclaim

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Message-ID: <20130517075019.GF25158@dhcp22.suse.cz>
Date:	Fri, 17 May 2013 09:50:19 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Glauber Costa <glommer@...allels.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Ying Han <yinghan@...gle.com>, Hugh Dickins <hughd@...gle.com>,
	Michel Lespinasse <walken@...gle.com>,
	Greg Thelen <gthelen@...gle.com>, Tejun Heo <tj@...nel.org>,
	Balbir Singh <bsingharora@...il.com>
Subject: Re: [patch v3 -mm 3/3] vmscan, memcg: Do softlimit reclaim also for
 targeted reclaim

On Wed 15-05-13 12:42:10, Glauber Costa wrote:
> On 05/13/2013 11:46 AM, Michal Hocko wrote:
> > Soft reclaim has been done only for the global reclaim (both background
> > and direct). Since "memcg: integrate soft reclaim tighter with zone
> > shrinking code" there is no reason for this limitation anymore as the
> > soft limit reclaim doesn't use any special code paths and it is a
> > part of the zone shrinking code which is used by both global and
> > targeted reclaims.
> > 
> > From semantic point of view it is even natural to consider soft limit
> > before touching all groups in the hierarchy tree which is touching the
> > hard limit because soft limit tells us where to push back when there is
> > a  memory pressure. It is not important whether the pressure comes from
> > the limit or imbalanced zones.
> > 
> > This patch simply enables soft reclaim unconditionally in
> > mem_cgroup_should_soft_reclaim so it is enabled for both global and
> > targeted reclaim paths. mem_cgroup_soft_reclaim_eligible needs to learn
> > about the root of the reclaim to know where to stop checking soft limit
> > state of parents up the hierarchy.
> > Say we have
> > A (over soft limit)
> >  \
> >   B (below s.l., hit the hard limit)
> >  / \
> > C   D (below s.l.)
> > 
> > B is the source of the outside memory pressure now for D but we
> > shouldn't soft reclaim it because it is behaving well under B subtree
> > and we can still reclaim from C (pressumably it is over the limit).
> > mem_cgroup_soft_reclaim_eligible should therefore stop climbing up the
> > hierarchy at B (root of the memory pressure).
> > 
> > Changes since v1
> > - add sc->target_mem_cgroup handling into mem_cgroup_soft_reclaim_eligible
> > 
> > Signed-off-by: Michal Hocko <mhocko@...e.cz>
> > ---
> 
> Reviewed-by: Glauber Costa <glommer@...nvz.org>

Thanks for the review Glauber!

-- 
Michal Hocko
SUSE Labs
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