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authorMel Gorman <mgorman@suse.de>2014-06-04 16:07:14 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-06-04 16:53:59 -0700
commit4f9b16a64753d0bb607454347036dc997fd03b82 (patch)
tree26169e829082644a3e6ee6bd4a9991b061425c50 /include
parent944d9fec8d7aee3f2e16573e9b6a16634b33f403 (diff)
downloadlinux-4f9b16a64753d0bb607454347036dc997fd03b82.tar.bz2
mm: disable zone_reclaim_mode by default
When it was introduced, zone_reclaim_mode made sense as NUMA distances punished and workloads were generally partitioned to fit into a NUMA node. NUMA machines are now common but few of the workloads are NUMA-aware and it's routine to see major performance degradation due to zone_reclaim_mode being enabled but relatively few can identify the problem. Those that require zone_reclaim_mode are likely to be able to detect when it needs to be enabled and tune appropriately so lets have a sensible default for the bulk of users. This patch (of 2): zone_reclaim_mode causes processes to prefer reclaiming memory from local node instead of spilling over to other nodes. This made sense initially when NUMA machines were almost exclusively HPC and the workload was partitioned into nodes. The NUMA penalties were sufficiently high to justify reclaiming the memory. On current machines and workloads it is often the case that zone_reclaim_mode destroys performance but not all users know how to detect this. Favour the common case and disable it by default. Users that are sophisticated enough to know they need zone_reclaim_mode will detect it. Signed-off-by: Mel Gorman <mgorman@suse.de> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Reviewed-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com> Acked-by: Michal Hocko <mhocko@suse.cz> Reviewed-by: Christoph Lameter <cl@linux.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include')
-rw-r--r--include/linux/topology.h3
1 files changed, 2 insertions, 1 deletions
diff --git a/include/linux/topology.h b/include/linux/topology.h
index 973671ff9e7d..dda6ee521e74 100644
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -58,7 +58,8 @@ int arch_update_cpu_topology(void);
/*
* If the distance between nodes in a system is larger than RECLAIM_DISTANCE
* (in whatever arch specific measurement units returned by node_distance())
- * then switch on zone reclaim on boot.
+ * and zone_reclaim_mode is enabled then the VM will only call zone_reclaim()
+ * on nodes within this distance.
*/
#define RECLAIM_DISTANCE 30
#endif