[PATCH] Optimize off-node performance of zone reclaim

Ensure that the performance of off node pages stays the same as before.
Off node pagefault tests showed an 18% drop in performance without this
patch.

- Increase the timeout to 30 seconds to reduce the overhead.

- Move all code possible out of the off node hot path for zone reclaim
  (Sorry Andrew, the struct initialization had to be sacrificed).
  The read_page_state() bit us there.

- Check first for the timeout before any other checks.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 15 insertions, 14 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2e34b61a70c7..465bfa54dfd6 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1589,24 +1589,20 @@ int zone_reclaim_mode __read_mostly;
 /*
  * Mininum time between zone reclaim scans
  */
-#define ZONE_RECLAIM_INTERVAL HZ/2
+#define ZONE_RECLAIM_INTERVAL 30*HZ
 /*
  * Try to free up some pages from this zone through reclaim.
  */
 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
 {
-        int nr_pages = 1 << order;
+        int nr_pages;
         struct task_struct *p = current;
         struct reclaim_state reclaim_state;
-        struct scan_control sc = {
-                .gfp_mask       = gfp_mask,
-                .may_writepage  = 0,
-                .may_swap       = 0,
-                .nr_mapped      = read_page_state(nr_mapped),
-                .nr_scanned     = 0,
-                .nr_reclaimed   = 0,
-                .priority       = 0
-        };
+        struct scan_control sc;
+
+        if (time_before(jiffies,
+                zone->last_unsuccessful_zone_reclaim + ZONE_RECLAIM_INTERVAL))
+                        return 0;
 
         if (!(gfp_mask & __GFP_WAIT) ||
                 zone->zone_pgdat->node_id != numa_node_id() ||
@@ -1614,12 +1610,17 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
                 atomic_read(&zone->reclaim_in_progress) > 0)
                         return 0;
 
-        if (time_before(jiffies,
-                zone->last_unsuccessful_zone_reclaim + ZONE_RECLAIM_INTERVAL))
-                        return 0;
+        sc.may_writepage = 0;
+        sc.may_swap = 0;
+        sc.nr_scanned = 0;
+        sc.nr_reclaimed = 0;
+        sc.priority = 0;
+        sc.nr_mapped = read_page_state(nr_mapped);
+        sc.gfp_mask = gfp_mask;
 
         disable_swap_token();
 
+        nr_pages = 1 << order;
         if (nr_pages > SWAP_CLUSTER_MAX)
                 sc.swap_cluster_max = nr_pages;
         else