From 27f10907b7cca57df5e2a9c94c14354dd1b7879d Mon Sep 17 00:00:00 2001
From: Anton Blanchard <anton@samba.org>
Date: Thu, 18 Feb 2010 12:29:23 +0000
Subject: powerpc/numa: Set a smaller value for RECLAIM_DISTANCE to enable zone
 reclaim

I noticed /proc/sys/vm/zone_reclaim_mode was 0 on a ppc64 NUMA box. It gets
enabled via this:

        /*
         * If another node is sufficiently far away then it is better
         * to reclaim pages in a zone before going off node.
         */
        if (distance > RECLAIM_DISTANCE)
                zone_reclaim_mode = 1;

Since we use the default value of 20 for REMOTE_DISTANCE and 20 for
RECLAIM_DISTANCE it never kicks in.

The local to remote bandwidth ratios can be quite large on System p
machines so it makes sense for us to reclaim clean pagecache locally before
going off node.

The patch below sets a smaller value for RECLAIM_DISTANCE and thus enables
zone reclaim.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---
 arch/powerpc/include/asm/topology.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

(limited to 'arch')

diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
index 8eaec310a25..a7d76949155 100644
--- a/arch/powerpc/include/asm/topology.h
+++ b/arch/powerpc/include/asm/topology.h
@@ -8,6 +8,16 @@ struct device_node;
 
 #ifdef CONFIG_NUMA
 
+/*
+ * Before going off node we want the VM to try and reclaim from the local
+ * node. It does this if the remote distance is larger than RECLAIM_DISTANCE.
+ * With the default REMOTE_DISTANCE of 20 and the default RECLAIM_DISTANCE of
+ * 20, we never reclaim and go off node straight away.
+ *
+ * To fix this we choose a smaller value of RECLAIM_DISTANCE.
+ */
+#define RECLAIM_DISTANCE 10
+
 #include <asm/mmzone.h>
 
 static inline int cpu_to_node(int cpu)
-- 
cgit v1.2.2