linux-kernel - Re: [PATCH] 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] [day] [month] [year] [list]

Message-ID: <20250312080102.GF19424@noisy.programming.kicks-ass.net>
Date: Wed, 12 Mar 2025 09:01:02 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Libo Chen <libo.chen@...cle.com>
Cc: mgorman@...hsingularity.net, linux-kernel@...r.kernel.org,
	mingo@...hat.com, tj@...nel.org, juri.lelli@...hat.com,
	vincent.guittot@...aro.org, akpm@...ux-foundation.org,
	longman@...hat.com, lorenzo.stoakes@...cle.com
Subject: Re: [PATCH] sched/numa: skip VMA scanning on memory pinned to one
 NUMA node via cpuset.mems

On Tue, Mar 11, 2025 at 09:04:47AM -0700, 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.

Its been a while since I looked at all this, but if we don't scan these
pages, then it will not account for these pages, and the pinned memory
will not become an attractor for the tasks that use this memory, right?

> 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);
> -- 
> 2.43.5
>