Re: [PATCH RFC 08/14] mm/huge_memory: mark PMD mappings of the huge zero folio special

[Oscar Salvador <osalvador@suse.de>]

On Tue, Jun 17, 2025 at 05:43:39PM +0200, David Hildenbrand wrote:
> The huge zero folio is refcounted (+mapcounted -- is that a word?)
> differently than "normal" folios, similarly (but different) to the ordinary
> shared zeropage.
> 
> For this reason, we special-case these pages in
> vm_normal_page*/vm_normal_folio*, and only allow selected callers to
> still use them (e.g., GUP can still take a reference on them).
> 
> vm_normal_page_pmd() already filters out the huge zero folio. However,
> so far we are not marking it as special like we do with the ordinary
> shared zeropage. Let's mark it as special, so we can further refactor
> vm_normal_page_pmd() and vm_normal_page().
> 
> While at it, update the doc regarding the shared zero folios.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>

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

While doing this, would it make sense to update vm_normal_page_pmd()
comments to refelect that pmd_special will also catch huge_zero_folio()?
It only mentions huge pfnmaps.

It might not be worth doing since you remove that code later on, but
maybe if someone stares at this commit alone..


-- 
Oscar Salvador
SUSE Labs