linux-kernel - [PATCH 17/19] Do not setup zonelist cache when there is only one node

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Message-Id: <1235477835-14500-18-git-send-email-mel@csn.ul.ie>
Date:	Tue, 24 Feb 2009 12:17:13 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Mel Gorman <mel@....ul.ie>,
	Linux Memory Management List <linux-mm@...ck.org>
Cc:	Pekka Enberg <penberg@...helsinki.fi>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lin Ming <ming.m.lin@...el.com>,
	Zhang Yanmin <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH 17/19] Do not setup zonelist cache when there is only one node

There is a zonelist cache which is used to track zones that are not in
the allowed cpuset or found to be recently full. This is to reduce cache
footprint on large machines. On smaller machines, it just incurs cost
for no gain. This patch only uses the zonelist cache when there are NUMA
nodes.

Signed-off-by: Mel Gorman <mel@....ul.ie>
---
 mm/page_alloc.c |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 73cf205..e598da8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1483,9 +1483,15 @@ this_zone_full:
 			zlc_mark_zone_full(zonelist, z);
 try_next_zone:
 		if (NUMA_BUILD && !did_zlc_setup) {
-			/* we do zlc_setup after the first zone is tried */
-			allowednodes = zlc_setup(zonelist, alloc_flags);
-			zlc_active = 1;
+			/*
+			 * we do zlc_setup after the first zone is tried
+			 * but only if there are multiple nodes to make
+			 * it worthwhile
+			 */
+			if (num_online_nodes() > 1) {
+				allowednodes = zlc_setup(zonelist, alloc_flags);
+				zlc_active = 1;
+			}
 			did_zlc_setup = 1;
 		}
 	}
-- 
1.5.6.5

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