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

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Date:	Tue, 27 Oct 2009 13:40:33 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Andrew Morton <akpm@...ux-foundation.org>, stable@...nel.org
Cc:	linux-kernel@...r.kernel.org,
	"linux-mm@...ck.org\"" <linux-mm@...ck.org>,
	Frans Pop <elendil@...net.nl>, Jiri Kosina <jkosina@...e.cz>,
	Sven Geggus <lists@...hsschwanzdomain.de>,
	Karol Lewandowski <karol.k.lewandowski@...il.com>,
	Tobias Oetiker <tobi@...iker.ch>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Rik van Riel <riel@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Stephan von Krawczynski <skraw@...net.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Mel Gorman <mel@....ul.ie>
Subject: [PATCH 3/3] vmscan: Force kswapd to take notice faster when high-order watermarks are being hit

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@....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

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