linux-kernel - Re: [PATCH v2 2/2] mm/compaction: avoid rescanning pageblocks in isolate

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Date:	Wed, 7 May 2014 14:47:05 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Vlastimil Babka <vbabka@...e.cz>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Greg Thelen <gthelen@...gle.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Minchan Kim <minchan@...nel.org>,
	Mel Gorman <mgorman@...e.de>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Christoph Lameter <cl@...ux.com>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH v2 2/2] mm/compaction: avoid rescanning pageblocks in
 isolate_freepages

On Wed, 7 May 2014, Vlastimil Babka wrote:

> The compaction free scanner in isolate_freepages() currently remembers PFN of
> the highest pageblock where it successfully isolates, to be used as the
> starting pageblock for the next invocation. The rationale behind this is that
> page migration might return free pages to the allocator when migration fails
> and we don't want to skip them if the compaction continues.
> 
> Since migration now returns free pages back to compaction code where they can
> be reused, this is no longer a concern. This patch changes isolate_freepages()
> so that the PFN for restarting is updated with each pageblock where isolation
> is attempted. Using stress-highalloc from mmtests, this resulted in 10%
> reduction of the pages scanned by the free scanner.
> 
> Note that the somewhat similar functionality that records highest successful
> pageblock in zone->compact_cached_free_pfn, remains unchanged. This cache is
> used when the whole compaction is restarted, not for multiple invocations of
> the free scanner during single compaction.
> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
> Cc: Michal Nazarewicz <mina86@...a86.com>
> Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> Cc: Christoph Lameter <cl@...ux.com>
> Cc: Rik van Riel <riel@...hat.com>

Acked-by: David Rientjes <rientjes@...gle.com>
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