mm/compaction: make isolate_freepages start at pageblock boundary (49e068f0) · Commits · 戴 / test

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:

Vlastimil Babka <vbabka@suse.cz> Reported-by:

Heesub Shin <heesub.shin@samsung.com> Acked-by:

Minchan Kim <minchan@kernel.org> Cc: Mel Gorman <mgorman@suse.de> Acked-by:

Joonsoo 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:

Rik 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:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

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;

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