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

[Christoph Hellwig]

On Wed, Nov 15, 2023 at 08:29:02PM -0500, Peter Xu wrote:
> Hugepd format is only used in PowerPC with hugetlbfs.  In commit
> a6e79df92e4a ("mm/gup: disallow FOLL_LONGTERM GUP-fast writing to
> file-backed mappings"), we added a check to fail gup-fast if there's
> potential risk of violating GUP over writeback file systems.  That should
> never apply to hugepd.
>
> Drop that check, not only because it'll never be true for hugepd, but also
> it paves way for reusing the function outside fast-gup.

What prevents us from ever using hugepd with file mappings?  I think
it would naturally fit in with how large folios for the pagecache work.

So keeping this check and generalizing it seems like the better idea to
me.