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

[Mel Gorman]

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@xxxxxxxxx>
---
 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

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