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

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Date:	Wed, 15 May 2013 12:42:10 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Michal Hocko <mhocko@...e.cz>
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 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>

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