Re: [PATCH v5 0/7] mm/mprotect: Fix dax puds

[Peter Xu <peterx@redhat.com>]

On Wed, Nov 13, 2024 at 05:42:15PM +0100, David Hildenbrand wrote:
> On 13.11.24 17:39, Peter Xu wrote:
> > On Mon, Nov 11, 2024 at 10:20:59PM +0100, Jann Horn wrote:
> > > On Mon, Aug 12, 2024 at 8:12 PM Peter Xu <peterx@redhat.com> wrote:
> > > > Dax supports pud pages for a while, but mprotect on puds was missing since
> > > > the start.  This series tries to fix that by providing pud handling in
> > > > mprotect().  The goal is to add more types of pud mappings like hugetlb or
> > > > pfnmaps.  This series paves way for it by fixing known pud entries.
> > > 
> > > Do people actually use hardware where they can use PUD THP mappings
> > > for DAX? I thought that was just some esoteric feature that isn't
> > > actually usable on almost any system.
> > > Was I wrong about that?
> > 
> > I did run it with a qemu emulated nvdimm device.  Though in reality I've no
> > idea on how many people are using it..
> 
> I wonder if we still have to support it ... or could disable it+rip it out.

Note that in my previous email, I also mentioned mremap() for PMD on dax
too.  If that's a real problem, it won't be fixed even if dropping dax PUD
support.

And we definitely want to understand whether there're still users on pud
dax to consider dropping anything.. it could still be that both mprotect()
and mremap() are not yet used in the current use cases.

Thanks,

-- 
Peter Xu