linux-kernel - Re: [PATCH] mm: compaction: Do not accidentally skip pageblocks in the migrate scanner

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Date:	Thu, 20 Dec 2012 17:45:50 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
CC:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: compaction: Do not accidentally skip pageblocks in
 the migrate scanner

On 12/20/2012 09:22 AM, Mel Gorman wrote:
> Compaction uses the ALIGN macro incorrectly with the migrate scanner by
> adding pageblock_nr_pages to a PFN. It happened to work when initially
> implemented as the starting PFN was also aligned but with caching restarts
> and isolating in smaller chunks this is no longer always true. The impact is
> that the migrate scanner scans outside its current pageblock. As pfn_valid()
> is still checked properly it does not cause any failure and the impact
> of the bug is that in some cases it will scan more than necessary when
> it crosses a page boundary but by no more than COMPACT_CLUSTER_MAX. It
> is highly unlikely this is even measurable but it's still wrong so this
> patch addresses the problem.
>
> Signed-off-by: Mel Gorman <mgorman@...e.de>

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

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