Re: [PATCH v2 3/3] mm/huge_memory: don't mark refcounted folios special in vmf_insert_folio_pud()

[Jason Gunthorpe]

On Wed, Jun 11, 2025 at 02:06:54PM +0200, David Hildenbrand wrote:
> Marking PUDs that map a "normal" refcounted folios as special is
> against our rules documented for vm_normal_page().
> 
> Fortunately, there are not that many pud_special() check that can be
> mislead and are right now rather harmless: e.g., none so far
> bases decisions whether to grab a folio reference on that decision.
> 
> Well, and GUP-fast will fallback to GUP-slow. All in all, so far no big
> implications as it seems.
> 
> Getting this right will get more important as we introduce
> folio_normal_page_pud() and start using it in more place where we
> currently special-case based on other VMA flags.
> 
> Fix it just like we fixed vmf_insert_folio_pmd().
> 
> Add folio_mk_pud() to mimic what we do with folio_mk_pmd().
> 
> Fixes: dbe54153296d ("mm/huge_memory: add vmf_insert_folio_pud()")
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
>  include/linux/mm.h | 19 ++++++++++++++++-
>  mm/huge_memory.c   | 51 +++++++++++++++++++++++++---------------------
>  2 files changed, 46 insertions(+), 24 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Jason