1 files changed, 14 insertions, 13 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index ff2ebe9458a3..5d4c4d02254d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1503,10 +1503,6 @@ module_init(kswapd_init)
  *
  * If non-zero call zone_reclaim when the number of free pages falls below
  * the watermarks.
- *
- * In the future we may add flags to the mode. However, the page allocator
- * should only have to check that zone_reclaim_mode != 0 before calling
- * zone_reclaim().
  */
 int zone_reclaim_mode __read_mostly;
 
@@ -1524,6 +1520,12 @@ int zone_reclaim_mode __read_mostly;
 #define ZONE_RECLAIM_PRIORITY 4
 
 /*
+ * Percentage of pages in a zone that must be unmapped for zone_reclaim to
+ * occur.
+ */
+int sysctl_min_unmapped_ratio = 1;
+
+/*
  * Try to free up some pages from this zone through reclaim.
  */
 static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
@@ -1590,18 +1592,17 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
         int node_id;
 
         /*
-         * Do not reclaim if there are not enough reclaimable pages in this
-         * zone that would satify this allocations.
+         * Zone reclaim reclaims unmapped file backed pages.
          *
-         * All unmapped pagecache pages are reclaimable.
-         *
-         * Both counters may be temporarily off a bit so we use
-         * SWAP_CLUSTER_MAX as the boundary. It may also be good to
-         * leave a few frequently used unmapped pagecache pages around.
+         * A small portion of unmapped file backed pages is needed for
+         * file I/O otherwise pages read by file I/O will be immediately
+         * thrown out if the zone is overallocated. So we do not reclaim
+         * if less than a specified percentage of the zone is used by
+         * unmapped file backed pages.
          */
         if (zone_page_state(zone, NR_FILE_PAGES) -
-                zone_page_state(zone, NR_FILE_MAPPED) < SWAP_CLUSTER_MAX)
-                        return 0;
+            zone_page_state(zone, NR_FILE_MAPPED) <= zone->min_unmapped_ratio)
+                return 0;
 
         /*
          * Avoid concurrent zone reclaims, do not reclaim in a zone that does