Re: [PATCH v4 3/4] mm: mprotect: convert to folio_needs_prot_numa()

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Mon, Oct 20, 2025 at 08:12:08PM +0200, David Hildenbrand wrote:
> On 20.10.25 19:49, Lorenzo Stoakes wrote:
> > On Mon, Oct 20, 2025 at 07:34:51PM +0200, David Hildenbrand wrote:
> > > On 20.10.25 17:14, Kefeng Wang wrote:
> > > >
> > > >
> > > > On 2025/10/20 21:10, Lorenzo Stoakes wrote:
> > > > > On Mon, Oct 20, 2025 at 02:18:44PM +0800, Kefeng Wang wrote:
> > > > > > The prot_numa_skip() naming is not good since it updates the folio
> > > > > > access time except checking whether to skip prot NUMA, so rename it
> > > > > > to folio_needs_prot_numa(), and cleanup it a bit, remove ret by
> > > > >
> > > > > Hmm not sure 'folio_needs_prot_numa()' is any better in terms of indicating
> > > > > that you're updating the access time to be honest.
> > > > >
> > > > > Also it seems to suggest that you're determining whether a mapping of the
> > > > > folio should be made a NUMA hint by the folio alone rather than the reality
> > > > > that the mapping is being considered for NUMA hinting and you're checking
> > > > > to see if you actually have to do it.
> > >
> > > ... because the folio doesn't need prot_none protection for NUMA hitning? :)
> >
> > folio_xxx() impliles to me that the folio independently has proeprty 'xxx'.
> >
>
> I would agree if it would be a folio_has_* or folio_test_*.

folio_is_zone_device()
folio_is_zone_movable()
folio_needs_release()
folio_needs_cow_for_dma()
folio_memcg_kmem()
folio_memcg_charged()
folio_pgoff()
folio_pos()
folio_contains()
folio_mapcount()

etc. etc. etc.

All properties of the folio in particular, not folio_has_*() or folio_test_*().

I mean the pattern is established in the kernel. Including folio_needs_*()!

I honestly wonder if the original formulation was correct - check for exemptions.

So something like folio_exempt_from_prot_numa()?

Or this way around folio_suitable_prot_numa()?

I think this is an English thing. 'folio needs prot numa' reads as 'this folio
_needs_ prot numa' right?

Oh - folio_can_map_prot_numa()? Something like this?

>
> To me the folio is really just the main entity we are querying information
> about. Not the VMA, not the target node, but the folio.

OK, I guess folio_needs_cow_for_dma() does the same thing with MMF_HAS_PINNED.

>
> > So it's like saying 'here's a folio, does it NEED prot numa?' right?
>
> I'd say: "here is a folio, does it need numa protection in this vma". So I
> still don't understand your point, unfortunately.

Again I think it's an English thing. As I said above.

>
> And keep disliking prot_numa_hint_needed() ;)

Well you are very particular about naming :)

I similarly dislike folio_needs_prot_numa()...

>
> But again, I won't fight for it if you have strong opinions on it.

It's not the biggest issue in the world. Equally if you insist I won't lose
sleep over this...

>
> It would be better if we could have discussed that as part of v2 to avoid
> having Kefeng go back and forth. Maybe v3+v4 were sent out a bit too quickly

At v2 I had just got back from holiday (+ being sick) and had a >1,000 mail
backlog, sorry.

>
> --
> Cheers
>
> David / dhildenb
>
>

Cheers, Lorenzo