linux-kernel - Re: [PATCH 6/7] mm: page allocator: Limit when direct reclaim is used when compaction is deferred

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Message-ID: <20111122175055.GE15253@barrios-laptop.redhat.com>
Date:	Wed, 23 Nov 2011 02:50:55 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linux-MM <linux-mm@...ck.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Jan Kara <jack@...e.cz>, Andy Isaacson <adi@...apodia.org>,
	Johannes Weiner <jweiner@...hat.com>,
	Rik van Riel <riel@...hat.com>, Nai Xia <nai.xia@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/7] mm: page allocator: Limit when direct reclaim is
 used when compaction is deferred

On Mon, Nov 21, 2011 at 06:36:47PM +0000, Mel Gorman wrote:
> If compaction is deferred, we enter direct reclaim to try reclaim the
> pages that way. For small high-orders, this has a reasonable chance
> of success. However, if the caller as specified __GFP_NO_KSWAPD to
> limit the disruption to the system, it makes more sense to fail the
> allocation rather than stall the caller in direct reclaim. This patch
> will skip direct reclaim if compaction is deferred and the caller
> specifies __GFP_NO_KSWAPD.
> 
> Async compaction only considers a subset of pages so it is possible for
> compaction to be deferred prematurely and not enter direct reclaim even
> in cases where it should. To compensate for this, this patch also defers
> compaction only if sync compaction failed.
> 
> Signed-off-by: Mel Gorman <mgorman@...e.de>
Acked-by: Minchan Kim <minchan.kim@...il.com>

It does make sense to me. 

-- 
Kind regards,
Minchan Kim
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