Re: [PATCH v1 1/2] mm/huge_memory: don't mark refcounted pages special in vmf_insert_folio_pmd()

[Oscar Salvador <osalvador@suse.de>]

On Tue, Jun 03, 2025 at 11:16:33PM +0200, David Hildenbrand wrote:
> Marking PMDs that map a "normal" refcounted folios as special is
> against our rules documented for vm_normal_page().
> 
> Fortunately, there are not that many pmd_special() check that can be
> mislead, and most vm_normal_page_pmd()/vm_normal_folio_pmd() users that
> would get this wrong right now are 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 use
> folio_normal_page_pmd() in more places.
> 
> Fix it by just inlining the relevant code, making the whole
> pmd_none() handling cleaner. We can now use folio_mk_pmd().
> 
> While at it, make sure that a pmd that is not-none is actually present
> before comparing PFNs.
> 
> Fixes: 6c88f72691f8 ("mm/huge_memory: add vmf_insert_folio_pmd()")
> Signed-off-by: David Hildenbrand <david@redhat.com>

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



-- 
Oscar Salvador
SUSE Labs