2 files changed, 19 insertions, 0 deletions

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index bd791e452ad7..67ab5febabf7 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -490,6 +490,12 @@ struct zone {
         unsigned long           managed_pages;
 
         /*
+         * Number of MIGRATE_RESEVE page block. To maintain for just
+         * optimization. Protected by zone->lock.
+         */
+        int                     nr_migrate_reserve_block;
+
+        /*
          * rarely used fields:
          */
         const char              *name;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5248fe070aa4..89d81f4429ca 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3901,6 +3901,7 @@ static void setup_zone_migrate_reserve(struct zone *zone)
         struct page *page;
         unsigned long block_migratetype;
         int reserve;
+        int old_reserve;
 
         /*
          * Get the start pfn, end pfn and the number of blocks to reserve
@@ -3922,6 +3923,12 @@ static void setup_zone_migrate_reserve(struct zone *zone)
          * future allocation of hugepages at runtime.
          */
         reserve = min(2, reserve);
+        old_reserve = zone->nr_migrate_reserve_block;
+
+        /* When memory hot-add, we almost always need to do nothing */
+        if (reserve == old_reserve)
+                return;
+        zone->nr_migrate_reserve_block = reserve;
 
         for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
                 if (!pfn_valid(pfn))
@@ -3959,6 +3966,12 @@ static void setup_zone_migrate_reserve(struct zone *zone)
                                 reserve--;
                                 continue;
                         }
+                } else if (!old_reserve) {
+                        /*
+                         * At boot time we don't need to scan the whole zone
+                         * for turning off MIGRATE_RESERVE.
+                         */
+                        break;
                 }
 
                 /*