linux-kernel - [PATCH v2 1/2] sched/numa: skip VMA scanning on memory pinned to one NUMA node via cpuset.mems

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250327002352.203332-2-libo.chen@oracle.com>
Date: Wed, 26 Mar 2025 17:23:51 -0700
From: Libo Chen <libo.chen@...cle.com>
To: peterz@...radead.org, mgorman@...hsingularity.net, longman@...hat.com
Cc: linux-kernel@...r.kernel.org, mingo@...hat.com, tj@...nel.org
Subject: [PATCH v2 1/2] sched/numa: skip VMA scanning on memory pinned to one NUMA node via cpuset.mems

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.

Signed-off-by: Libo Chen <libo.chen@...cle.com>
---
 kernel/sched/fair.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e43993a4e5807..6f405e00c9c7e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3329,6 +3329,13 @@ static void task_numa_work(struct callback_head *work)
 	if (p->flags & PF_EXITING)
 		return;

+	/*
+	 * Memory is pinned to only one NUMA node via cpuset.mems, naturally
+	 * no page can be migrated.
+	 */
+	if (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);
-- 
2.43.5