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

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Message-ID: <825fb8bc-91ca-4de4-9c8d-44590b6c1cba@redhat.com>
Date: Tue, 11 Mar 2025 13:42:53 -0400
From: Waiman Long <llong@...hat.com>
To: Libo Chen <libo.chen@...cle.com>, peterz@...radead.org,
 mgorman@...hsingularity.net
Cc: linux-kernel@...r.kernel.org, mingo@...hat.com, tj@...nel.org,
 juri.lelli@...hat.com, vincent.guittot@...aro.org,
 akpm@...ux-foundation.org, lorenzo.stoakes@...cle.com
Subject: Re: [PATCH] sched/numa: skip VMA scanning on memory pinned to one
 NUMA node via cpuset.mems

On 3/11/25 12:04 PM, Libo Chen wrote:
> 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.
>
> 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 c798d27952431..ec4749a7be33a 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3315,6 +3315,13 @@ 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);

Do you have any performance improvement data that can be included in the 
commit log?

Cheers,
Longman