1 files changed, 30 insertions, 9 deletions

diff --git a/mm/compaction.c b/mm/compaction.c
index 5039c964f5c8..b69b7dac0361 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -330,7 +330,7 @@ static bool suitable_migration_target(struct page *page)
  * (even though it may still end up isolating some pages).
  */
 static unsigned long isolate_freepages_block(struct compact_control *cc,
-                                unsigned long blockpfn,
+                                unsigned long *start_pfn,
                                 unsigned long end_pfn,
                                 struct list_head *freelist,
                                 bool strict)
@@ -339,6 +339,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
         struct page *cursor, *valid_page = NULL;
         unsigned long flags;
         bool locked = false;
+        unsigned long blockpfn = *start_pfn;
 
         cursor = pfn_to_page(blockpfn);
 
@@ -415,6 +416,9 @@ isolate_fail:
 
         }
 
+        /* Record how far we have got within the block */
+        *start_pfn = blockpfn;
+
         trace_mm_compaction_isolate_freepages(nr_scanned, total_isolated);
 
         /*
@@ -463,14 +467,16 @@ isolate_freepages_range(struct compact_control *cc,
 
         for (; pfn < end_pfn; pfn += isolated,
                                 block_end_pfn += pageblock_nr_pages) {
+                /* Protect pfn from changing by isolate_freepages_block */
+                unsigned long isolate_start_pfn = pfn;
 
                 block_end_pfn = min(block_end_pfn, end_pfn);
 
                 if (!pageblock_pfn_to_page(pfn, block_end_pfn, cc->zone))
                         break;
 
-                isolated = isolate_freepages_block(cc, pfn, block_end_pfn,
-                                                   &freelist, true);
+                isolated = isolate_freepages_block(cc, &isolate_start_pfn,
+                                                block_end_pfn, &freelist, true);
 
                 /*
                  * In strict mode, isolate_freepages_block() returns 0 if
@@ -769,6 +775,7 @@ static void isolate_freepages(struct compact_control *cc)
         struct zone *zone = cc->zone;
         struct page *page;
         unsigned long block_start_pfn;  /* start of current pageblock */
+        unsigned long isolate_start_pfn; /* exact pfn we start at */
         unsigned long block_end_pfn;    /* end of current pageblock */
         unsigned long low_pfn;       /* lowest pfn scanner is able to scan */
         int nr_freepages = cc->nr_freepages;
@@ -777,14 +784,15 @@ static void isolate_freepages(struct compact_control *cc)
         /*
          * Initialise the free scanner. The starting point is where we last
          * 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
+         * zone when isolating for the first time. For looping we also need
+         * this pfn aligned down to the pageblock boundary, because we do
          * block_start_pfn -= pageblock_nr_pages in the for loop.
          * For ending point, take care when isolating in last pageblock of a
          * a zone which ends in the middle of a pageblock.
          * The low boundary is the end of the pageblock the migration scanner
          * is using.
          */
+        isolate_start_pfn = cc->free_pfn;
         block_start_pfn = cc->free_pfn & ~(pageblock_nr_pages-1);
         block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
                                                 zone_end_pfn(zone));
@@ -797,7 +805,8 @@ static void isolate_freepages(struct compact_control *cc)
          */
         for (; block_start_pfn >= low_pfn && cc->nr_migratepages > nr_freepages;
                                 block_end_pfn = block_start_pfn,
-                                block_start_pfn -= pageblock_nr_pages) {
+                                block_start_pfn -= pageblock_nr_pages,
+                                isolate_start_pfn = block_start_pfn) {
                 unsigned long isolated;
 
                 /*
@@ -822,13 +831,25 @@ static void isolate_freepages(struct compact_control *cc)
                 if (!isolation_suitable(cc, page))
                         continue;
 
-                /* Found a block suitable for isolating free pages from */
-                cc->free_pfn = block_start_pfn;
-                isolated = isolate_freepages_block(cc, block_start_pfn,
+                /* Found a block suitable for isolating free pages from. */
+                isolated = isolate_freepages_block(cc, &isolate_start_pfn,
                                         block_end_pfn, freelist, false);
                 nr_freepages += isolated;
 
                 /*
+                 * Remember where the free scanner should restart next time,
+                 * which is where isolate_freepages_block() left off.
+                 * But if it scanned the whole pageblock, isolate_start_pfn
+                 * now points at block_end_pfn, which is the start of the next
+                 * pageblock.
+                 * In that case we will however want to restart at the start
+                 * of the previous pageblock.
+                 */
+                cc->free_pfn = (isolate_start_pfn < block_end_pfn) ?
+                                isolate_start_pfn :
+                                block_start_pfn - pageblock_nr_pages;
+
+                /*
                  * Set a flag that we successfully isolated in this pageblock.
                  * In the next loop iteration, zone->compact_cached_free_pfn
                  * will not be updated and thus it will effectively contain the