linux-kernel - Re: [PATCH 09/11] mm: vmscan: When reclaiming for compaction, ensure there are sufficient free pages available

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Date:	Thu, 15 Dec 2011 23:35:34 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Dave Jones <davej@...hat.com>, Jan Kara <jack@...e.cz>,
	Andy Isaacson <adi@...apodia.org>,
	Johannes Weiner <jweiner@...hat.com>,
	Nai Xia <nai.xia@...il.com>, Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 09/11] mm: vmscan: When reclaiming for compaction, ensure
 there are sufficient free pages available

On 12/14/2011 10:41 AM, Mel Gorman wrote:
> In commit [e0887c19: vmscan: limit direct reclaim for higher order
> allocations], Rik noted that reclaim was too aggressive when THP was
> enabled. In his initial patch he used the number of free pages to
> decide if reclaim should abort for compaction. My feedback was that
> reclaim and compaction should be using the same logic when deciding if
> reclaim should be aborted.
>
> Unfortunately, this had the effect of reducing THP success rates when
> the workload included something like streaming reads that continually
> allocated pages. The window during which compaction could run and return
> a THP was too small.
>
> This patch combines Rik's two patches together. compaction_suitable()
> is still used to decide if reclaim should be aborted to allow
> compaction is used. However, it will also ensure that there is a
> reasonable buffer of free pages available. This improves upon the
> THP allocation success rates but bounds the number of pages that are
> freed for compaction.
>
> Signed-off-by: Mel Gorman<mgorman@...e.de>

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

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