Re: [PATCH RFC 06/12] mm/gup: Drop folio_fast_pin_allowed() in hugepd processing

[Matthew Wilcox]

On Wed, Nov 22, 2023 at 12:00:24AM -0800, Christoph Hellwig wrote:
> > The other option is I can always add a comment above gup_huge_pd()
> > explaining this special bit, so that when someone is adding hugepd support
> > to file large folios we'll hopefully not forget it?  But then that
> > generalization work will only happen when the code will be needed.
> 
> If dropping the check is the right thing for now (and I think the ppc
> maintainers and willy as the large folio guy might have a more useful
> opinions than I do), leaving a comment in would be very useful.

It looks like ARM (in the person of Ryan) are going to add support for
something equivalent to hugepd.  Insofar as I understand hugepd, anyway.
I've done my best to set up the generic code so that the arch code can
use whatever size TLB entries it supports.  I haven't been looking to the
hugetlb code as a reference for it, since it can assume natural alignment
and generic THP/large folio must be able to handle arbitrary alignment.

If powerpc want to join in on the fun, they're more than welcome, but I
get the feeling that investment in Linux-on-PPC is somewhat smaller than
Linux-on-ARM these days.  Even if we restrict that to the server space.