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

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Message-ID: <CAEwNFnBSg71QoLZbOqZbXK3fGEGneituU3PmiYTAw1VM3KcwcQ@mail.gmail.com>
Date:	Wed, 31 Aug 2011 19:13:34 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Johannes Weiner <jweiner@...hat.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 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>

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.

-- 
Kind regards,
Minchan Kim
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