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powerpc/numa: Set a smaller value for RECLAIM_DISTANCE to enable zone reclaim

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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>
This commit is contained in:
Anton Blanchard 2010-02-18 12:29:23 +00:00 committed by Benjamin Herrenschmidt
parent 7429b3842c
commit 27f10907b7
1 changed files with 10 additions and 0 deletions
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10
arch/powerpc/include/asm/topology.h
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@ -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)