Re: [RFC PATCH v2 34/47] hugetlb: userfaultfd: add support for high-granularity UFFDIO_CONTINUE

[Peter Xu]

On Tue, Dec 27, 2022 at 11:38:31AM -0500, James Houghton wrote:
> On Fri, Dec 23, 2022 at 1:38 PM Peter Xu <peterx@xxxxxxxxxx> wrote:
> >
> > James,
> >
> > On Fri, Oct 21, 2022 at 04:36:50PM +0000, James Houghton wrote:
> > > +     bool use_hgm = uffd_ctx_has_hgm(&dst_vma->vm_userfaultfd_ctx) &&
> > > +             mode == MCOPY_ATOMIC_CONTINUE;
> >
> > Do you think in your new version use_hgm can work even for MISSING by
> > default?
> 
> I don't think so -- UFFDIO_COPY will allocate a hugepage, so I'm not
> sure if it makes sense to allow it at high-granularity. If UFFDIO_COPY
> didn't allocate a new page, then it could make sense (maybe we'd need
> a new ioctl or new UFFDIO_COPY mode?). I think it makes most sense to
> add this with another series.

I forgot again on how the page cache is managed for the split pages,
sorry..  Yeah let's stick with minor mode for now.

-- 
Peter Xu