path: root/mm
diff options
authorShaohua Li <>2011-08-25 15:59:12 -0700
committerLinus Torvalds <>2011-08-25 16:25:34 -0700
commit439423f6894aa0dec22187526827456f5004baed (patch)
tree1f22238a24b83e0beb1467a1f73b0db952c69894 /mm
parent4c30c6f566c0989ddaee3407da44751e340a63ed (diff)
vmscan: clear ZONE_CONGESTED for zone with good watermark
ZONE_CONGESTED is only cleared in kswapd, but pages can be freed in any task. It's possible ZONE_CONGESTED isn't cleared in some cases: 1. the zone is already balanced just entering balance_pgdat() for order-0 because concurrent tasks free memory. In this case, later check will skip the zone as it's balanced so the flag isn't cleared. 2. high order balance fallbacks to order-0. quote from Mel: At the end of balance_pgdat(), kswapd uses the following logic; If reclaiming at high order { for each zone { if all_unreclaimable skip if watermark is not met order = 0 loop again /* watermark is met */ clear congested } } i.e. it clears ZONE_CONGESTED if it the zone is balanced. if not, it restarts balancing at order-0. However, if the higher zones are balanced for order-0, kswapd will miss clearing ZONE_CONGESTED as that only happens after a zone is shrunk. This can mean that wait_iff_congested() stalls unnecessarily. This patch makes kswapd clear ZONE_CONGESTED during its initial highmem->dma scan for zones that are already balanced. Signed-off-by: Shaohua Li <> Acked-by: Mel Gorman <> Reviewed-by: Minchan Kim <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'mm')
1 files changed, 3 insertions, 0 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 22631e0994b3..b7719ec10dc5 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2529,6 +2529,9 @@ loop_again:
high_wmark_pages(zone), 0, 0)) {
end_zone = i;
+ } else {
+ /* If balanced, clear the congested flag */
+ zone_clear_flag(zone, ZONE_CONGESTED);
if (i < 0)