Re: [PATCH RFC 10/14] mm/memory: factor out common code from vm_normal_page_*()

[Oscar Salvador <osalvador@suse.de>]

On Tue, Jun 17, 2025 at 05:43:41PM +0200, David Hildenbrand wrote:
> Let's reduce the code duplication and factor out the non-pte/pmd related
> magic into vm_normal_page_pfn().
> 
> To keep it simpler, check the pfn against both zero folios. We could
> optimize this, but as it's only for the !CONFIG_ARCH_HAS_PTE_SPECIAL
> case, it's not a compelling micro-optimization.
> 
> With CONFIG_ARCH_HAS_PTE_SPECIAL we don't have to check anything else,
> really.
> 
> It's a good question if we can even hit the !CONFIG_ARCH_HAS_PTE_SPECIAL
> scenario in the PMD case in practice: but doesn't really matter, as
> it's now all unified in vm_normal_page_pfn().
> 
> While at it, add a check that pmd_special() is really only set where we
> would expect it.
> 
> No functional change intended.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>

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

Comment below

>  struct folio *vm_normal_folio(struct vm_area_struct *vma, unsigned long addr,
> @@ -650,35 +661,12 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
>  {
>  	unsigned long pfn = pmd_pfn(pmd);
>  
> -	/* Currently it's only used for huge pfnmaps */

Although the check kind of spells it out, we could leave this one and also add
that huge_zero_pfn, to make it more explicit.
 

-- 
Oscar Salvador
SUSE Labs