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Patch "mm, numa: really disable NUMA balancing by default on single node machines" has been added to the 3.14-stable tree

PATCH [email protected] 1 participant 1 message Jun 3, 2015

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Stable branch Memory management MM NUMA placement
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This is a note to let you know that I've just added the patch titled

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

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-numa-really-disable-numa-balancing-by-default-on-single-node-machines.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From b0dc2b9bb4ab782115b964310518ee0b17784277 Mon Sep 17 00:00:00 2001

From: Mel Gorman <[email protected]>
Date: Thu, 14 May 2015 15:17:09 -0700
Subject: mm, numa: really disable NUMA balancing by default on single node machines

From: Mel Gorman <[email protected]>

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 <[email protected]>
Reviewed-by Rik van Riel <[email protected]>
Signed-off-by Andrew Morton <[email protected]>
Signed-off-by Linus Torvalds <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 mm/mempolicy.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
mm/mempolicy.c +1 -1
@@ -2663,7 +2663,7 @@ static void __init check_numabalancing_e
 	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",

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/mm-numa-really-disable-numa-balancing-by-default-on-single-node-machines.patch