Re: [PATCH v2 3/3] mm/khugepaged: release contended mmap read lock after scanning enough VMAs

[Lorenzo Stoakes (ARM)]

On Fri, Nov 06, 2026 at 11:29:00AM +0100, Jose A. Perez de Azpillaga wrote:
> >> with pages_to_scan below 4 the batch is 0, so under constant contention
> >> we keep dropping the lock at the cursor and never scan anything, don't we?
> >
> > This feels like repackaged AI review...
> >
> > The mmap lock won't be eternally contended and if it is, with pages_to_scan
> > under 4, I think that's fine.
> >
> > Alternatively could make that >= an == and the post-++ a pre-++ and the 0 will
> > never be hit in this case.
> >
> > Or could have a minimum cap.
>
> with >= a minimum cap needs to be 2, since the cursor can stop at hend
> inside the VMA we just scanned and the walk lands on it again after the
> drop. with == only batch - 1 VMAs get scanned per cycle, so a batch of 1
> scans nothing, today's batch-0 loop at pages_to_scan 4..7, and a batch
> of 2 hits the hend case. it's safe from 3 up.

Please don't copy/paste LLM responses. I'm sure it's in good faith, but it's not
helpful. I will run any changes through AI myself.

--
Cheers, Lorenzo