+ sched-numa-skip-vma-scanning-on-memory-pinned-to-one-numa-node-via-cpusetmems.patch added to mm-new branch

[Andrew Morton <akpm@linux-foundation.org>]

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The patch titled
     Subject: sched/numa: skip VMA scanning on memory pinned to one NUMA node via cpuset.mems
has been added to the -mm mm-new branch.  Its filename is
     sched-numa-skip-vma-scanning-on-memory-pinned-to-one-numa-node-via-cpusetmems.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/sched-numa-skip-vma-scanning-on-memory-pinned-to-one-numa-node-via-cpusetmems.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Libo Chen <libo.chen@oracle.com>
Subject: sched/numa: skip VMA scanning on memory pinned to one NUMA node via cpuset.mems
Date: Thu, 17 Apr 2025 12:15:42 -0700

Patch series "sched/numa: Skip VMA scanning on memory pinned", v4.


This patch (of 2):

When the memory of the current task is pinned to one NUMA node by cgroup,
there is no point in continuing the rest of VMA scanning and hinting page
faults as they will just be overhead.  With this change, there will be no
more unnecessary PTE updates or page faults in this scenario.

We have seen up to a 6x improvement on a typical java workload running on
VMs with memory and CPU pinned to one NUMA node via cpuset in a two-socket
AARCH64 system.  With the same pinning, on a 18-cores-per-socket Intel
platform, we have seen 20% improvment in a microbench that creates a
30-vCPU selftest KVM guest with 4GB memory, where each vCPU reads 4KB
pages in a fixed number of loops.

Link: https://lkml.kernel.org/r/20250417191543.1781862-1-libo.chen@oracle.com
Link: https://lkml.kernel.org/r/20250417191543.1781862-2-libo.chen@oracle.com
Signed-off-by: Libo Chen <libo.chen@oracle.com>
Cc: "Chen, Tim C" <tim.c.chen@intel.com>
Cc: Chen, Yu C <yu.c.chen@intel.com>
Cc: Chris Hyser <chris.hyser@oracle.com>
Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Madadi Vineeth Reddy <vineethr@linux.ibm.com>
Cc: Mel Gorman <mgorman <mgorman@suse.de>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Raghavendra K T <raghavendra.kt@amd.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/sched/fair.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/kernel/sched/fair.c~sched-numa-skip-vma-scanning-on-memory-pinned-to-one-numa-node-via-cpusetmems
+++ a/kernel/sched/fair.c
@@ -3329,6 +3329,13 @@ static void task_numa_work(struct callba
 	if (p->flags & PF_EXITING)
 		return;
 
+	/*
+	 * Memory is pinned to only one NUMA node via cpuset.mems, naturally
+	 * no page can be migrated.
+	 */
+	if (cpusets_enabled() && nodes_weight(cpuset_current_mems_allowed) == 1)
+		return;
+
 	if (!mm->numa_next_scan) {
 		mm->numa_next_scan = now +
 			msecs_to_jiffies(sysctl_numa_balancing_scan_delay);
_

Patches currently in -mm which might be from libo.chen@oracle.com are

sched-numa-skip-vma-scanning-on-memory-pinned-to-one-numa-node-via-cpusetmems.patch
sched-numa-add-tracepoint-that-tracks-the-skipping-of-numa-balancing-due-to-cpuset-memory-pinning.patch