linux-kernel - Re: [patch] memcg: skip scanning active lists based on individual size

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Date:	Wed, 31 Aug 2011 14:30:51 +0200
From:	Johannes Weiner <jweiner@...hat.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Balbir Singh <bsingharora@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] memcg: skip scanning active lists based on individual
 size

On Wed, Aug 31, 2011 at 07:13:34PM +0900, Minchan Kim wrote:
> On Wed, Aug 31, 2011 at 6:08 PM, Johannes Weiner <jweiner@...hat.com> wrote:
> > Reclaim decides to skip scanning an active list when the corresponding
> > inactive list is above a certain size in comparison to leave the
> > assumed working set alone while there are still enough reclaim
> > candidates around.
> >
> > The memcg implementation of comparing those lists instead reports
> > whether the whole memcg is low on the requested type of inactive
> > pages, considering all nodes and zones.
> >
> > This can lead to an oversized active list not being scanned because of
> > the state of the other lists in the memcg, as well as an active list
> > being scanned while its corresponding inactive list has enough pages.
> >
> > Not only is this wrong, it's also a scalability hazard, because the
> > global memory state over all nodes and zones has to be gathered for
> > each memcg and zone scanned.
> >
> > Make these calculations purely based on the size of the two LRU lists
> > that are actually affected by the outcome of the decision.
> >
> > Signed-off-by: Johannes Weiner <jweiner@...hat.com>
> > Cc: Rik van Riel <riel@...hat.com>
> > Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> > Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > Cc: Daisuke Nishimura <nishimura@....nes.nec.co.jp>
> > Cc: Balbir Singh <bsingharora@...il.com>
> 
> Reviewed-by: Minchan Kim <minchan.kim@...il.com>

Thank you.

> I can't understand why memcg is designed for considering all nodes and zones.
> Is it a mistake or on purpose?
> Maybe Kame or Balbir can answer it.
> 
> Anyway, this change does make sense to me.
> 
> Nitpick: Please remove inactive_ratio in Documentation/cgroups/memory.txt.
> I think it would be better to separate it into another patch.

Good catch.

---
Subject: [patch] memcg: skip scanning active lists based on individual fix

Also ditch the documentation note for the removed stats value.

Signed-off-by: Johannes Weiner <jweiner@...hat.com>
---

diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
index 06eb6d9..cc0ebc5 100644
--- a/Documentation/cgroups/memory.txt
+++ b/Documentation/cgroups/memory.txt
@@ -418,7 +418,6 @@ total_unevictable	- sum of all children's "unevictable"
 
 # The following additional stats are dependent on CONFIG_DEBUG_VM.
 
-inactive_ratio		- VM internal parameter. (see mm/page_alloc.c)
 recent_rotated_anon	- VM internal parameter. (see mm/vmscan.c)
 recent_rotated_file	- VM internal parameter. (see mm/vmscan.c)
 recent_scanned_anon	- VM internal parameter. (see mm/vmscan.c)
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