On 1/30/12 1:09 AM, Mel Gorman wrote:

quoted

The migrate_pfn is just below a memory hole and the free scanner is
beyond the hole. When isolate_migratepages started, it scans from
migrate_pfn to migrate_pfn+pageblock_nr_pages which is now in a memory
hole. It checks pfn_valid() on the first PFN but then scans into the
hole where there are not necessarily valid struct pages.

This patch ensures that isolate_migratepages calls pfn_valid when
necessary.

Signed-off-by: Mel Gorman <mgorman@suse.de>

If anyone cares, this looks good to me, so:

Acked-by: Michal Nazarewicz <redacted>

quoted

---
 mm/compaction.c |   13 +++++++++++++
 1 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 899d956..edc1e26 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c

@@ -313,6 +313,19 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
 		} else if (!locked)
 			spin_lock_irq(&zone->lru_lock);

+		/*
+		 * migrate_pfn does not necessarily start aligned to a
+		 * pageblock. Ensure that pfn_valid is called when moving
+		 * into a new MAX_ORDER_NR_PAGES range in case of large
+		 * memory holes within the zone
+		 */
+		if ((low_pfn & (MAX_ORDER_NR_PAGES - 1)) == 0) {
+			if (!pfn_valid(low_pfn)) {
+				low_pfn += MAX_ORDER_NR_PAGES - 1;
+				continue;
+			}
+		}
+
 		if (!pfn_valid_within(low_pfn))
 			continue;
 		nr_scanned++;

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
ooo +----<email/xmpp: mpn@google.com>--------------ooO--(_)--Ooo--

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