[PATCH] vmscan: avoid bogus throttling

- If max_scan evaluates to zero due to a very small inactive list and high
  `priority' numbers, we don't want to thrlttle yet.

- In balance_pgdat(), we may end up not scanning any pages because all
  zones happened to be above pages_high.  Avoid throttling in this case too.

diff --git a/mm/vmscan.c b/mm/vmscan.c
index ba9be09720888753bee7e0e138dc4d697d42b3ff..33d83aa788e5b96983a1eed7db5b60fe0366db01 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -870,7 +870,8 @@ int try_to_free_pages(struct zone **zones,
                wakeup_bdflush(total_scanned);
 
                /* Take a nap, wait for some writeback to complete */
-               blk_congestion_wait(WRITE, HZ/10);
+               if (total_scanned)
+                       blk_congestion_wait(WRITE, HZ/10);
        }
        if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY))
                out_of_memory();
@@ -915,6 +916,7 @@ static int balance_pgdat(pg_data_t *pgdat, int nr_pages, struct page_state *ps)
 
        for (priority = DEF_PRIORITY; priority; priority--) {
                int all_zones_ok = 1;
+               int pages_scanned = 0;
 
                for (i = 0; i < pgdat->nr_zones; i++) {
                        struct zone *zone = pgdat->node_zones + i;
@@ -933,6 +935,7 @@ static int balance_pgdat(pg_data_t *pgdat, int nr_pages, struct page_state *ps)
                        max_scan = zone->nr_inactive >> priority;
                        reclaimed = shrink_zone(zone, max_scan, GFP_KERNEL,
                                        &total_scanned, ps);
+                       total_scanned += pages_scanned;
                        reclaim_state->reclaimed_slab = 0;
                        shrink_slab(total_scanned, GFP_KERNEL);
                        reclaimed += reclaim_state->reclaimed_slab;
@@ -950,7 +953,8 @@ static int balance_pgdat(pg_data_t *pgdat, int nr_pages, struct page_state *ps)
                 * OK, kswapd is getting into trouble.  Take a nap, then take
                 * another pass across the zones.
                 */
-               blk_congestion_wait(WRITE, HZ/10);
+               if (pages_scanned)
+                       blk_congestion_wait(WRITE, HZ/10);
        }
 
        for (i = 0; i < pgdat->nr_zones; i++) {