[PATCH] powerpc/mm: Fix RECLAIM_DISTANCE

[Gavin Shan]

When @node_reclaim_mode ("/proc/sys/vm/zone_reclaim_mode") is enabled,
the nodes in the specified distance (< RECLAIM_DISTANCE) to the preferred
one will be checked for page direct reclaim in the fast path, as below
function call chain indicates. Currently, RECLAIM_DISTANCE is set to 10,
equal to LOCAL_DISTANCE. It means no nodes, including the preferred one,
don't match the conditions. So no nodes are checked for direct reclaim
in the fast path.

   __alloc_pages_nodemask
   get_page_from_freelist
   zone_allows_reclaim

This fixes it by setting RECLAIM_DISTANCE to 30. With it, the preferred
node and its directly adjacent nodes will be checked for page direct
reclaim. The comments explaining RECLAIM_DISTANCE is out of date. This
updates and makes it correct.

Signed-off-by: Gavin Shan <gwshan at linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/topology.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
index 8b3b46b..ce1a156 100644
--- a/arch/powerpc/include/asm/topology.h
+++ b/arch/powerpc/include/asm/topology.h
@@ -9,10 +9,11 @@ struct device_node;
 #ifdef CONFIG_NUMA
 
 /*
- * If zone_reclaim_mode is enabled, a RECLAIM_DISTANCE of 10 will mean that
- * all zones on all nodes will be eligible for zone_reclaim().
+ * If node_reclaim_mode is enabled, a RECLAIM_DISTANCE of 30 means that
+ * the preferred node and its directly adjacent nodes are eligible for
+ * node_reclaim().
  */
-#define RECLAIM_DISTANCE 10
+#define RECLAIM_DISTANCE	30
 
 #include <asm/mmzone.h>
 
-- 
2.7.4