1 files changed, 28 insertions, 26 deletions

diff --git a/mm/compaction.c b/mm/compaction.c
index b6984e234fdf..bcce7897e17a 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -384,6 +384,20 @@ static bool suitable_migration_target(struct page *page)
 }
 
 /*
+ * Returns the start pfn of the last page block in a zone.  This is the starting
+ * point for full compaction of a zone.  Compaction searches for free pages from
+ * the end of each zone, while isolate_freepages_block scans forward inside each
+ * page block.
+ */
+static unsigned long start_free_pfn(struct zone *zone)
+{
+        unsigned long free_pfn;
+        free_pfn = zone->zone_start_pfn + zone->spanned_pages;
+        free_pfn &= ~(pageblock_nr_pages-1);
+        return free_pfn;
+}
+
+/*
  * Based on information in the current compact_control, find blocks
  * suitable for isolating free pages from and then isolate them.
  */
@@ -422,17 +436,6 @@ static void isolate_freepages(struct zone *zone,
                                         pfn -= pageblock_nr_pages) {
                 unsigned long isolated;
 
-                /*
-                 * Skip ahead if another thread is compacting in the area
-                 * simultaneously. If we wrapped around, we can only skip
-                 * ahead if zone->compact_cached_free_pfn also wrapped to
-                 * above our starting point.
-                 */
-                if (cc->order > 0 && (!cc->wrapped ||
-                                      zone->compact_cached_free_pfn >
-                                      cc->start_free_pfn))
-                        pfn = min(pfn, zone->compact_cached_free_pfn);
-
                 if (!pfn_valid(pfn))
                         continue;
 
@@ -474,7 +477,15 @@ static void isolate_freepages(struct zone *zone,
                  */
                 if (isolated) {
                         high_pfn = max(high_pfn, pfn);
-                        if (cc->order > 0)
+
+                        /*
+                         * If the free scanner has wrapped, update
+                         * compact_cached_free_pfn to point to the highest
+                         * pageblock with free pages. This reduces excessive
+                         * scanning of full pageblocks near the end of the
+                         * zone
+                         */
+                        if (cc->order > 0 && cc->wrapped)
                                 zone->compact_cached_free_pfn = high_pfn;
                 }
         }
@@ -484,6 +495,11 @@ static void isolate_freepages(struct zone *zone,
 
         cc->free_pfn = high_pfn;
         cc->nr_freepages = nr_freepages;
+
+        /* If compact_cached_free_pfn is reset then set it now */
+        if (cc->order > 0 && !cc->wrapped &&
+                        zone->compact_cached_free_pfn == start_free_pfn(zone))
+                zone->compact_cached_free_pfn = high_pfn;
 }
 
 /*
@@ -570,20 +586,6 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
         return ISOLATE_SUCCESS;
 }
 
-/*
- * Returns the start pfn of the last page block in a zone.  This is the starting
- * point for full compaction of a zone.  Compaction searches for free pages from
- * the end of each zone, while isolate_freepages_block scans forward inside each
- * page block.
- */
-static unsigned long start_free_pfn(struct zone *zone)
-{
-        unsigned long free_pfn;
-        free_pfn = zone->zone_start_pfn + zone->spanned_pages;
-        free_pfn &= ~(pageblock_nr_pages-1);
-        return free_pfn;
-}
-
 static int compact_finished(struct zone *zone,
                             struct compact_control *cc)
 {