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authorMel Gorman <mgorman@suse.de>2015-05-14 15:17:09 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-06-06 08:21:05 -0700
commitf138997c09631f1cf6e58a85fa2dda088e3c0c49 (patch)
tree82640936243035fa72a44d66f07f705d85621903
parent54651d44ef59cd8c66845a15d59dac8d7cc10c39 (diff)
mm, numa: really disable NUMA balancing by default on single node machines
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@suse.de> Reviewed-by: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--mm/mempolicy.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index de5dc5e..0f7d73b 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2517,7 +2517,7 @@ 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) {
pr_info("%s automatic NUMA balancing. "
"Configure with numa_balancing= or the "
"kernel.numa_balancing sysctl",