From: Mel Gorman <mgorman@xxxxxxx>
3.12-stable review patch. If anyone has any objections, please let me know.
===============
commit b0dc2b9bb4ab782115b964310518ee0b17784277 upstream.
NUMA balancing is meant to be disabled by default on UMA machines but
the check is using nr_node_ids (highest node) instead of
num_online_nodes (online nodes).
The consequences are that a UMA machine with a node ID of 1 or higher
will enable NUMA balancing. This will incur useless overhead due to
minor faults with the impact depending on the workload. These are the
impact on the stats when running a kernel build on a single node machine
whose node ID happened to be 1:
vanilla patched
NUMA base PTE updates 5113158 0
NUMA huge PMD updates 643 0
NUMA page range updates 5442374 0
NUMA hint faults 2109622 0
NUMA hint local faults 2109622 0
NUMA hint local percent 100 100
NUMA pages migrated 0 0
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
mm/mempolicy.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index e63ade49ea24..51cd7d066e0f 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2589,7 +2589,7 @@ static void __init check_numabalancing_enable(void)
if (numabalancing_override)
set_numabalancing_state(numabalancing_override == 1);
- if (nr_node_ids > 1 && !numabalancing_override) {
+ if (num_online_nodes() > 1 && !numabalancing_override) {
printk(KERN_INFO "%s automatic NUMA balancing. "
"Configure with numa_balancing= or sysctl",
numabalancing_default ? "Enabling" : "Disabling");
--
2.4.2
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