linux-kernel - Re: [PATCH 2/2] memcg, vmscan: Fix forced scan of anonymous pages

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Message-ID: <20140731150653.GA9952@cmpxchg.org>
Date:	Thu, 31 Jul 2014 11:06:53 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	Jerome Marchand <jmarchan@...hat.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...e.cz>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 2/2] memcg, vmscan: Fix forced scan of anonymous pages

On Thu, Jul 31, 2014 at 01:49:45PM +0200, Jerome Marchand wrote:
> When memory cgoups are enabled, the code that decides to force to scan
> anonymous pages in get_scan_count() compares global values (free,
> high_watermark) to a value that is restricted to a memory cgroup
> (file). It make the code over-eager to force anon scan.
> 
> For instance, it will force anon scan when scanning a memcg that is
> mainly populated by anonymous page, even when there is plenty of file
> pages to get rid of in others memcgs, even when swappiness == 0. It
> breaks user's expectation about swappiness and hurts performance. 
> 
> This patch make sure that forced anon scan only happens when there not
> enough file pages for the all zone, not just in one random memcg.
> 
> Signed-off-by: Jerome Marchand <jmarchan@...hat.com>

Acked-by: Johannes Weiner <hannes@...xchg.org>
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