Re: [PATCH v2 4/4] sched/numa: do not let VMA PID activity gate promotion

[Gregory Price]

On Fri, Sep 18, 2026 at 03:01:34PM +0200, David Hildenbrand (Arm) wrote:
> > -		/* VMA scan is complete, do not scan until next sequence. */
> > +		/*
> > +		 * VMA scan is complete, do not scan until next sequence.  A
> > +		 * promotion-only scan reached the end of the VMA but did not
> > +		 * sample placement, so it does not count towards the starvation
> > +		 * horizon in vma_is_accessed().
> > +		 */
> >  		vma->numab_state->prev_scan_seq = mm->numa_scan_seq;
> > +		if (!promo_only)
> > +			vma->numab_state->prev_placement_scan_seq = mm->numa_scan_seq;
> 
> 
> This is all rather ... messy. I mean, just look at that promo_only() computation ...
> 
> There must be a cleaner way ;)

I tried 3 or 4 different ways, this is the least ugly thing I could come
up with :\

The scan sequence thing is particularly confusing, and numab=3 mode
(NORMAL|TIERING) makes trying to reason about this whole thing really
painful.

I can see about making it at least a bit easier on the eyes.

~Gregory