Messages in this thread Patch in this message | | | Date | Wed, 13 May 2015 09:10:53 +0100 | From | Mel Gorman <> | Subject | [PATCH] mm, numa: Really disable NUMA balancing by default on single node machines |
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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> Cc: <stable@vger.kernel.org> #v3.8+ --- mm/mempolicy.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/mempolicy.c b/mm/mempolicy.c index ede26291d4aa..747743237d9f 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -2518,7 +2518,7 @@ 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",
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