linux-kernel - Re: [PATCH] doc: describe memcg swappiness more precisely memory.swappiness==0

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Date:	Tue, 16 Oct 2012 09:51:03 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Michal Hocko <mhocko@...e.cz>
CC:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	David Rientjes <rientjes@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] doc: describe memcg swappiness more precisely memory.swappiness==0

(2012/10/16 7:07), Michal Hocko wrote:
> And a follow up for memcg.swappiness documentation which is more
> specific about spwappiness==0 meaning.
> ---
>  From 1bc3a94fea728107ed108edd42df464b908cd067 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@...e.cz>
> Date: Mon, 15 Oct 2012 11:43:56 +0200
> Subject: [PATCH] doc: describe memcg swappiness more precisely
>
> since fe35004f (mm: avoid swapping out with swappiness==0) memcg reclaim
> stopped swapping out anon pages completely when 0 value is used.
> Although this is somehow expected it hasn't been done for a really long
> time this way and so it is probably better to be explicit about the
> effect. Moreover global reclaim swapps out even when swappiness is 0
> to prevent from OOM killer.
>
> Signed-off-by: Michal Hocko <mhocko@...e.cz>

Nice :)
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

> ---
>   Documentation/cgroups/memory.txt |    4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
> index c07f7b4..71c4da4 100644
> --- a/Documentation/cgroups/memory.txt
> +++ b/Documentation/cgroups/memory.txt
> @@ -466,6 +466,10 @@ Note:
>   5.3 swappiness
>
>   Similar to /proc/sys/vm/swappiness, but affecting a hierarchy of groups only.
> +Please note that unlike the global swappiness, memcg knob set to 0
> +really prevents from any swapping even if there is a swap storage
> +available. This might lead to memcg OOM killer if there are no file
> +pages to reclaim.
>
>   Following cgroups' swappiness can't be changed.
>   - root cgroup (uses /proc/sys/vm/swappiness).
>


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