Re: [PATCH v3 3/3] mm/huge_memory: don't mark refcounted folios special in vmf_insert_folio_pud()

[Oscar Salvador <osalvador@suse.de>]

On Fri, Jun 13, 2025 at 11:27:02AM +0200, David Hildenbrand wrote:
> Marking PUDs that map a "normal" refcounted folios as special is
> against our rules documented for vm_normal_page(). normal (refcounted)
> folios shall never have the page table mapping marked as special.
> 
> 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()")
> Reviewed-by: Dan Williams <dan.j.williams@intel.com>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> Tested-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Oscar Salvador <osalvador@suse.de>



-- 
Oscar Salvador
SUSE Labs