Re: [PATCH RFC v2 11/18] mm: skip zeroing in vma_alloc_zeroed_movable_folio for pre-zeroed pages

["David Hildenbrand (Arm)" <david@kernel.org>]

On 4/20/26 14:50, Michael S. Tsirkin wrote:
> Use vma_alloc_folio_hints() and check PGHINT_ZEROED to skip
> clear_user_highpage() when the page is already zeroed.
> 
> On x86, vma_alloc_zeroed_movable_folio is overridden by a macro
> that uses __GFP_ZERO directly, so this change has no effect there.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> Assisted-by: Claude:claude-opus-4-6
> Assisted-by: cursor-agent:GPT-5.4-xhigh
> ---
>  include/linux/highmem.h | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
> index af03db851a1d..8bb67772c1cb 100644
> --- a/include/linux/highmem.h
> +++ b/include/linux/highmem.h
> @@ -321,9 +321,11 @@ struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
>  				   unsigned long vaddr)
>  {
>  	struct folio *folio;
> +	pghint_t hints;
>  
> -	folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, vaddr);
> -	if (folio && user_alloc_needs_zeroing())
> +	folio = vma_alloc_folio_hints(GFP_HIGHUSER_MOVABLE, 0, vma, vaddr,
> +				      &hints);
> +	if (folio && user_alloc_needs_zeroing() && !(hints & PGHINT_ZEROED))
>  		clear_user_highpage(&folio->page, vaddr);
>  
>  	return folio;


For others reading along, the variant on your other branch:

diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index af03db851a1d9..ffa683f64f1d1 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -320,13 +320,8 @@ static inline
 struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
 				   unsigned long vaddr)
 {
-	struct folio *folio;
-
-	folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, vaddr);
-	if (folio && user_alloc_needs_zeroing())
-		clear_user_highpage(&folio->page, vaddr);
-
-	return folio;
+	return vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO,
+			      0, vma, vaddr);
 }
 #endif

Looks like an extremely clean interface.

-- 
Cheers,

David