[PATCH 3/3] vmscan: Force kswapd to take notice faster when high-order watermarks are being hit

Mel Gorman
2009-10-27T13:40:41Z

When a high-order allocation fails, kswapd is kicked so that it reclaims
at a higher-order to avoid direct reclaimers stall and to help GFP_ATOMIC
allocations. Something has changed in recent kernels that affect the timing
where high-order GFP_ATOMIC allocations are now failing with more frequency,
particularly under pressure. This patch forces kswapd to notice sooner that
high-order allocations are occuring.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
---
mm/vmscan.c | 9 +++++++++
1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 64e4388..7eceb02 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2016,6 +2016,15 @@ loop_again:
priority != DEF_PRIORITY)
continue;

+ /*
+ * Exit the function now and have kswapd start over
+ * if it is known that higher orders are required
+ */
+ if (pgdat->kswapd_max_order > order) {
+ all_zones_ok = 1;
+ goto out;
+ }
+
if (!zone_watermark_ok(zone, order,
high_wmark_pages(zone), end_zone, 0))
all_zones_ok = 0;
--
1.6.3.3