linux-kernel - Re: [PATCH 1/2] mm/compaction: make isolate

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Message-ID: <20140416234309.GE27534@bbox>
Date:	Thu, 17 Apr 2014 08:43:09 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Heesub Shin <heesub.shin@...sung.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Dongjun Shin <d.j.shin@...sung.com>,
	Sunghwan Yun <sunghwan.yun@...sung.com>,
	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 1/2] mm/compaction: make isolate_freepages start at
 pageblock boundary

On Tue, Apr 15, 2014 at 11:18:26AM +0200, Vlastimil Babka wrote:
> The compaction freepage scanner implementation in isolate_freepages() starts
> by taking the current cc->free_pfn value as the first pfn. In a for loop, it
> scans from this first pfn to the end of the pageblock, and then subtracts
> pageblock_nr_pages from the first pfn to obtain the first pfn for the next
> for loop iteration.
> 
> This means that when cc->free_pfn starts at offset X rather than being aligned
> on pageblock boundary, the scanner will start at offset X in all scanned
> pageblock, ignoring potentially many free pages. Currently this can happen when
> a) zone's end pfn is not pageblock aligned, or
> b) through zone->compact_cached_free_pfn with CONFIG_HOLES_IN_ZONE enabled and
>    a hole spanning the beginning of a pageblock
> 
> This patch fixes the problem by aligning the initial pfn in isolate_freepages()
> to pageblock boundary. This also allows to replace the end-of-pageblock
> alignment within the for loop with a simple pageblock_nr_pages increment.
> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> Reported-by: Heesub Shin <heesub.shin@...sung.com>

Acked-by: Minchan Kim <minchan@...nel.org>

-stable stuff?

-- 
Kind regards,
Minchan Kim
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