From c946ee4ab03e6bf3c7b92435aaf65ef29f561e4a Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@suse.cz>
Date: Thu, 8 Dec 2011 14:34:27 -0800
Subject: [PATCH] --- yaml --- r: 276543 b: refs/heads/master c:
 d021563888312018ca65681096f62e36c20e63cc h: refs/heads/master i:   276541:
 53df1bf4e50319f57092dc9f0e95f28433a2a6da   276539:
 a9bd711fa279e36bc5fdf1865de0249c90b4ac51   276535:
 752692aaf0b4650815cde5137023fad5e50b5ecd   276527:
 66cc7b13448382fb9b4db1b597e72aa2e5dde080   276511:
 a156f5cdef7467bf5dd38c4bf1ae1b63966ccc07   276479:
 fb4d3be6a95f9de1b4e69d9f5ccc5225b084aa7d v: v3

---
 [refs]                | 2 +-
 trunk/mm/page_alloc.c | 8 +++++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/[refs] b/[refs]
index bb93a0bcb68a..423009b226da 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 09761333ed47e899cc1482c13090b95f3f711971
+refs/heads/master: d021563888312018ca65681096f62e36c20e63cc
diff --git a/trunk/mm/page_alloc.c b/trunk/mm/page_alloc.c
index 850009a7101e..2b8ba3aebf6e 100644
--- a/trunk/mm/page_alloc.c
+++ b/trunk/mm/page_alloc.c
@@ -3377,9 +3377,15 @@ static void setup_zone_migrate_reserve(struct zone *zone)
 	unsigned long block_migratetype;
 	int reserve;
 
-	/* Get the start pfn, end pfn and the number of blocks to reserve */
+	/*
+	 * Get the start pfn, end pfn and the number of blocks to reserve
+	 * We have to be careful to be aligned to pageblock_nr_pages to
+	 * make sure that we always check pfn_valid for the first page in
+	 * the block.
+	 */
 	start_pfn = zone->zone_start_pfn;
 	end_pfn = start_pfn + zone->spanned_pages;
+	start_pfn = roundup(start_pfn, pageblock_nr_pages);
 	reserve = roundup(min_wmark_pages(zone), pageblock_nr_pages) >>
 							pageblock_order;