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

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Date:	Mon, 15 Oct 2012 10:25:14 -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

> diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
> index 078701f..308fd77 100644
> --- a/Documentation/sysctl/vm.txt
> +++ b/Documentation/sysctl/vm.txt
> @@ -640,6 +640,9 @@ swappiness
>  This control is used to define how aggressive the kernel will swap
>  memory pages.  Higher values will increase agressiveness, lower values
>  decrease the amount of swap.
> +The value can be used from the [0, 100] range, where 0 means no swapping
> +at all (even if there is a swap storage enabled) while 100 means that
> +anonymous pages are reclaimed in the same rate as file pages.

I think this only correct when memcg. Even if swappiness==0, global reclaim swap
out anon pages before oom.

see below.

get_scan_count()
(snip)
	if (global_reclaim(sc)) {
		free  = zone_page_state(zone, NR_FREE_PAGES);
		/* If we have very few page cache pages,
		   force-scan anon pages. */
		if (unlikely(file + free <= high_wmark_pages(zone))) {
			fraction[0] = 1;
			fraction[1] = 0;
			denominator = 1;
			goto out;
		}
	}
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