linux-kernel - Re: [PATCH 05/11] mm: compaction: Determine if dirty pages can be migrated without blocking within ->migratepage

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Message-ID: <4EEABBE3.1050309@redhat.com>
Date:	Thu, 15 Dec 2011 22:32:51 -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 05/11] mm: compaction: Determine if dirty pages can be
 migrated without blocking within ->migratepage

On 12/14/2011 10:41 AM, Mel Gorman wrote:
> Asynchronous compaction is used when allocating transparent hugepages
> to avoid blocking for long periods of time. Due to reports of
> stalling, there was a debate on disabling synchronous compaction
> but this severely impacted allocation success rates. Part of the
> reason was that many dirty pages are skipped in asynchronous compaction
> by the following check;
>
> 	if (PageDirty(page)&&  !sync&&
> 		mapping->a_ops->migratepage != migrate_page)
> 			rc = -EBUSY;
>
> This skips over all mapping aops using buffer_migrate_page()
> even though it is possible to migrate some of these pages without
> blocking. This patch updates the ->migratepage callback with a "sync"
> parameter. It is the responsibility of the callback to fail gracefully
> if migration would block.
>
> Signed-off-by: Mel Gorman<mgorman@...e.de>

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

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