Re: [PATCH v5 05/15] mm/frame-vector: Use FOLL_LONGTERM

[John Hubbard]

On 11/5/20 4:49 AM, Jason Gunthorpe wrote:
> On Thu, Nov 05, 2020 at 10:25:24AM +0100, Daniel Vetter wrote:
> > > /*
> > >   * If we can't determine whether or not a pte is special, then fail immediately
> > >   * for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not
> > >   * to be special.
> > >   *
> > >   * For a futex to be placed on a THP tail page, get_futex_key requires a
> > >   * get_user_pages_fast_only implementation that can pin pages. Thus it's still
> > >   * useful to have gup_huge_pmd even if we can't operate on ptes.
> > >   */
> >
> > We support hugepage faults in gpu drivers since recently, and I'm not
> > seeing a pud_mkhugespecial anywhere. So not sure this works, but probably
> > just me missing something again.
>
> It means ioremap can't create an IO page PUD, it has to be broken up.
>
> Does ioremap even create anything larger than PTEs?

From my reading, yes. See ioremap_try_huge_pmd().

thanks,
--
John Hubbard
NVIDIA