1 files changed, 12 insertions, 10 deletions

diff --git a/mm/compaction.c b/mm/compaction.c
index 37f976287068..627dc2e4320f 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -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;