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List: linuxppc-embedded
Subject: [PATCH 1/3] powerpc: Set a smaller value for RECLAIM_DISTANCE to
From: Anton Blanchard <anton () samba ! org>
Date: 2010-04-30 4:33:24
Message-ID: 20100430043324.GB4622 () kryten
[Download RAW message or body]
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>
---
Index: powerpc.git/arch/powerpc/include/asm/topology.h
===================================================================
--- powerpc.git.orig/arch/powerpc/include/asm/topology.h 2010-02-18 14:26:45.736821967 +1100
+++ powerpc.git/arch/powerpc/include/asm/topology.h 2010-02-18 14:51:24.793071748 +1100
@@ -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)
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