Re: [PATCH 1/6] sched/numa: clear fault locality state on execve

[Gregory Price <gourry@gourry.net>]

On Wed, Oct 14, 2026 at 05:43:42PM +0800, Li Zhe wrote:
> task_numa_free(p, false) is used by execve() to reset NUMA balancing
> state without freeing p->numa_faults, because concurrent readers may
> still observe the task.
> 

Is a process that exec()'s going to run long enough to actually collect
any real numa fault data?

> the retained p->numa_faults array, but leaves the current-window buffer
> half and p->numa_faults_locality unchanged. Those are also NUMA fault
> feedback consumed by task_numa_placement() and update_task_scan_period(),
> so a newly executed image can inherit stale fault feedback from the old
> image.

I'm not sure this actually corrects much unless you have a long running
program that eventually exec()'s - and even then it seems like this all
self-corrects within a couple seconds.

Do you have some clear reproduction that makes an obvious wrong effect,
or was this just some static analysis?

It's "not wrong", but I'm trying to understand what impact this actually
has.

> The non-final path clears p->total_numa_faults and the averaged half of
> 
> Clear the whole retained p->numa_faults array and p->numa_faults_locality
> together in the non-final reset path.
> 
> Fixes: 04bb2f947505 ("sched/numa: Adjust scan rate in task_numa_placement")
> Signed-off-by: Li Zhe <lizhe.67@bytedance.com>
> ---
>  kernel/sched/fair.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 57360f5cdde4..1053437933ee 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4177,8 +4177,9 @@ void task_numa_free(struct task_struct *p, bool final)
>  		kfree(numa_faults);
>  	} else {
>  		p->total_numa_faults = 0;
> -		for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++)
> -			numa_faults[i] = 0;
> +		memset(p->numa_faults_locality, 0, sizeof(p->numa_faults_locality));
> +		memset(numa_faults, 0, sizeof(*numa_faults) *
> +		       NR_NUMA_HINT_FAULT_BUCKETS * nr_node_ids);
>  	}
>  }
>  
> -- 
> 2.20.1