[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>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2e34b61a70c727afc2895529c1997a1a8d399eee..465bfa54dfd6c8a5298cf48b1d906ec0461beba2 100644 (file)
--- 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