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Date:	Thu, 22 May 2014 12:04:12 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Dave Chinner <david@...morbit.com>,
	Yuanhan Liu <yuanhan.liu@...ux.intel.com>,
	Bob Liu <bob.liu@...cle.com>, Jan Kara <jack@...e.cz>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>,
	Linux-FSDevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 3/3] mm: vmscan: Use proportional scanning during direct
 reclaim and full scan at DEF_PRIORITY

On 05/22/2014 05:09 AM, Mel Gorman wrote:
> Commit "mm: vmscan: obey proportional scanning requirements for kswapd"
> ensured that file/anon lists were scanned proportionally for reclaim from
> kswapd but ignored it for direct reclaim. The intent was to minimse direct
> reclaim latency but Yuanhan Liu pointer out that it substitutes one long
> stall for many small stalls and distorts aging for normal workloads like
> streaming readers/writers.  Hugh Dickins pointed out that a side-effect of
> the same commit was that when one LRU list dropped to zero that the entirety
> of the other list was shrunk leading to excessive reclaim in memcgs.
> This patch scans the file/anon lists proportionally for direct reclaim
> to similarly age page whether reclaimed by kswapd or direct reclaim but
> takes care to abort reclaim if one LRU drops to zero after reclaiming the
> requested number of pages.
> 

> Note that there are fewer allocation stalls even though the amount
> of direct reclaim scanning is very approximately the same.
> 
> Signed-off-by: Mel Gorman <mgorman@...e.de>

Acked-by: Rik van Riel <riel@...hat.com>


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