Re: [PATCH v5 5/7] sched/numa: scan PID-inactive VMAs for promotion

[Gregory Price (Meta)]

On 2026-11-10 10:04 -0500, Gregory Price (Meta) wrote:
... snip ...

Sashiko report feedback
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4249,7 +4249,7 @@ static bool vma_needs_placement_scan(struct vm_area_struct *vma)
>  	 * threads can help scan this vma, force a vma scan.
>  	 */
>  	if (READ_ONCE(mm->numa_scan_seq) >
> -	   (vma->numab_state->prev_scan_seq + get_nr_threads(current)))
> +	   (vma->numab_state->prev_placement_scan_seq + get_nr_threads(current)))
>  		return true;
... snip ...
> +		if (placement_scan)
> +			vma->numab_state->prev_placement_scan_seq = mm->numa_scan_seq;

Sashiko took issue with these skips, but its reported impact is
overstated.  It tries to point out a pre-existing condition:

  prev_scan_seq skips an update on a rare corner condition, but
  now the same skip applies to prev_placement_scan_seq.

In modes 1 (placement) and 2 (tiering), the behavior is exactly the
same as it was.

In mode 3 (placement + tiering) the result is that the starvation
counter isn't reset - but everything still works anyway because the
VMA is still being scanned.

I can follow up with *another* commit, but it's really low impact.
Not sure it's worth the churn.

-- 
~Gregory