From 56608209d34b8add40af54031d4e420afbcde9f6 Mon Sep 17 00:00:00 2001 From: Anton Blanchard Date: Sun, 16 May 2010 20:19:56 +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 Signed-off-by: Benjamin Herrenschmidt diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h index 84ad11f..32adf72 100644 --- a/arch/powerpc/include/asm/topology.h +++ b/arch/powerpc/include/asm/topology.h @@ -18,6 +18,16 @@ struct device_node; */ #define RECLAIM_DISTANCE 10 +/* + * 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 static inline int cpu_to_node(int cpu) -- cgit v0.10.2