Messages in this thread | | | Date | Thu, 28 Mar 2024 11:10:59 +0100 | Subject | Re: [PATCH v4 06/13] mm/gup: Drop folio_fast_pin_allowed() in hugepd processing | From | David Hildenbrand <> |
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On 27.03.24 16:23, peterx@redhat.com wrote: > From: Peter Xu <peterx@redhat.com> > > Hugepd format for GUP is only used in PowerPC with hugetlbfs. There are > some kernel usage of hugepd (can refer to hugepd_populate_kernel() for > PPC_8XX), however those pages are not candidates for GUP. > > Commit a6e79df92e4a ("mm/gup: disallow FOLL_LONGTERM GUP-fast writing to > file-backed mappings") 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. Considering that hugepd is an old format (and even > software-only), there's no plan to extend hugepd into other file typed > memories that is prone to the same issue. > > Drop that check, not only because it'll never be true for hugepd per any > known plan, but also it paves way for reusing the function outside > fast-gup. > > To make sure we'll still remember this issue just in case hugepd will be > extended to support non-hugetlbfs memories, add a rich comment above > gup_huge_pd(), explaining the issue with proper references. > > Cc: Christoph Hellwig <hch@infradead.org> > Cc: Lorenzo Stoakes <lstoakes@gmail.com> > Cc: Michael Ellerman <mpe@ellerman.id.au> > Cc: linuxppc-dev@lists.ozlabs.org > Signed-off-by: Peter Xu <peterx@redhat.com> > ---
@Andrew, you properly adjusted the code to remove the gup_fast_folio_allowed() call instead of the folio_fast_pin_allowed() call, but
(1) the commit subject (2) comment for gup_huge_pd()
Still mention folio_fast_pin_allowed().
The patch "mm/gup: handle hugepd for follow_page()" then moves that (outdated) comment.
-- Cheers,
David / dhildenb
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