linux-kernel - Re: [RFC PATCH] memcg: oom: fix totalpages calculation for swappiness==0

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Date:	Mon, 15 Oct 2012 18:33:12 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-mm@...ck.org, David Rientjes <rientjes@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] memcg: oom: fix totalpages calculation for swappiness==0

>> I think this only correct when memcg. Even if swappiness==0, global reclaim swap
>> out anon pages before oom.
>
> Right you are (we really do swap when the file pages are really
> low)! Sorry about the confusion. I kind of became if(global_reclaim)
> block blind...
>
> Then this really needs a memcg specific documentation fix. What about
> the following?
> ---
> From 59a60705abd2faf9e266a4270bbf302001845588 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>
> ---
>  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.

Pretty good to me. Thank you!

Acked-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
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