Commit 597bb175 authored by Mel Gorman's avatar Mel Gorman Committed by Luis Henriques

mm, numa: really disable NUMA balancing by default on single node machines

commit b0dc2b9b 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: default avatarMel Gorman <mgorman@suse.de>
Reviewed-by: default avatarRik van Riel <riel@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent 6dbab50c
...@@ -2560,7 +2560,7 @@ static void __init check_numabalancing_enable(void) ...@@ -2560,7 +2560,7 @@ static void __init check_numabalancing_enable(void)
if (numabalancing_override) if (numabalancing_override)
set_numabalancing_state(numabalancing_override == 1); 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. " pr_info("%s automatic NUMA balancing. "
"Configure with numa_balancing= or the " "Configure with numa_balancing= or the "
"kernel.numa_balancing sysctl", "kernel.numa_balancing sysctl",
......
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