From 314b9cf3be0a02e5866f2a45e1d259cbff042dc2 Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Thu, 14 May 2015 15:17:09 -0700 Subject: mm, numa: really disable NUMA balancing by default on single node machines [ Upstream commit b0dc2b9bb4ab782115b964310518ee0b17784277 ] 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 Reviewed-by: Rik van Riel Cc: [3.8+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- mm/mempolicy.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/mempolicy.c b/mm/mempolicy.c index e58725aff7e9..39198cb78c6f 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -2548,7 +2548,7 @@ 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", -- cgit v1.2.3