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Commit 49e068f0 authored by Vlastimil Babka's avatar Vlastimil Babka Committed by Linus Torvalds
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mm/compaction: make isolate_freepages start at pageblock boundary 



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 permits replacing
the end-of-pageblock alignment within the for loop with a simple
pageblock_nr_pages increment.

Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
Reported-by: default avatarHeesub Shin <heesub.shin@samsung.com>
Acked-by: default avatarMinchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@suse.de>
Acked-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Michal Nazarewicz <mina86@mina86.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Christoph Lameter <cl@linux.com>
Acked-by: default avatarRik van Riel <riel@redhat.com>
Cc: Dongjun Shin <d.j.shin@samsung.com>
Cc: Sunghwan Yun <sunghwan.yun@samsung.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 0e3b7e54

mm/compaction.c

+12 −10
Original line number Diff line number Diff line
@@ -671,16 +671,20 @@ static void isolate_freepages(struct zone *zone, 
				struct compact_control *cc)

{

	struct page *page;

	unsigned long high_pfn, low_pfn, pfn, z_end_pfn, end_pfn;

	unsigned long high_pfn, low_pfn, pfn, z_end_pfn;

	int nr_freepages = cc->nr_freepages;

	struct list_head *freelist = &cc->freepages;



	/*

	 * Initialise the free scanner. The starting point is where we last

	 * scanned from (or the end of the zone if starting). The low point

	 * is the end of the pageblock the migration scanner is using.

	 * successfully isolated from, zone-cached value, or the end of the

	 * zone when isolating for the first time. We need this aligned to

	 * the pageblock boundary, because we do pfn -= pageblock_nr_pages

	 * in the for loop.

	 * The low boundary is the end of the pageblock the migration scanner

	 * is using.

	 */

	pfn = cc->free_pfn;

	pfn = cc->free_pfn & ~(pageblock_nr_pages-1);

	low_pfn = ALIGN(cc->migrate_pfn + 1, pageblock_nr_pages);



	/*
@@ -700,6 +704,7 @@ static void isolate_freepages(struct zone *zone, 
	for (; pfn >= low_pfn && cc->nr_migratepages > nr_freepages;

					pfn -= pageblock_nr_pages) {

		unsigned long isolated;

		unsigned long end_pfn;



		/*

		 * This can iterate a massively long zone without finding any
@@ -734,13 +739,10 @@ static void isolate_freepages(struct zone *zone, 
		isolated = 0;



		/*

		 * As pfn may not start aligned, pfn+pageblock_nr_page

		 * may cross a MAX_ORDER_NR_PAGES boundary and miss

		 * a pfn_valid check. Ensure isolate_freepages_block()

		 * only scans within a pageblock

		 * Take care when isolating in last pageblock of a zone which

		 * ends in the middle of a pageblock.

		 */

		end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);

		end_pfn = min(end_pfn, z_end_pfn);

		end_pfn = min(pfn + pageblock_nr_pages, z_end_pfn);

		isolated = isolate_freepages_block(cc, pfn, end_pfn,

						   freelist, false);

		nr_freepages += isolated;