linux-kernel - Re: [PATCH 04/10] mm: vmscan: Decide whether to compact the pgdat based on reclaim progress

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Message-ID: <51677599.6030000@redhat.com>
Date:	Thu, 11 Apr 2013 22:46:49 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Zlatko Calusic <zcalusic@...sync.net>,
	Johannes Weiner <hannes@...xchg.org>,
	dormando <dormando@...ia.net>,
	Satoru Moriya <satoru.moriya@....com>,
	Michal Hocko <mhocko@...e.cz>, Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/10] mm: vmscan: Decide whether to compact the pgdat
 based on reclaim progress

On 04/09/2013 07:06 AM, Mel Gorman wrote:
> In the past, kswapd makes a decision on whether to compact memory after the
> pgdat was considered balanced. This more or less worked but it is late to
> make such a decision and does not fit well now that kswapd makes a decision
> whether to exit the zone scanning loop depending on reclaim progress.
>
> This patch will compact a pgdat if at least the requested number of pages
> were reclaimed from unbalanced zones for a given priority. If any zone is
> currently balanced, kswapd will not call compaction as it is expected the
> necessary pages are already available.
>
> Signed-off-by: Mel Gorman <mgorman@...e.de>

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

This has the potential to increase kswapd cpu use, but probably at
the benefit of making reclaim run a little more smoothly. It should
help that compaction is only called when enough pages have been
freed.

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