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 4/21/26 12:58, David Hildenbrand (Arm) wrote:
> 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.
> 

And we could likely just do the following on top I assume.

diff --git a/arch/m68k/include/asm/page_no.h b/arch/m68k/include/asm/page_no.h
index d2532bc407ef..f511b763a235 100644
--- a/arch/m68k/include/asm/page_no.h
+++ b/arch/m68k/include/asm/page_no.h
@@ -12,9 +12,6 @@ extern unsigned long memory_end;
 
 #define copy_user_page(to, from, vaddr, pg)    copy_page(to, from)
 
-#define vma_alloc_zeroed_movable_folio(vma, vaddr) \
-       vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO, 0, vma, vaddr)
-
 #define __pa(vaddr)            ((unsigned long)(vaddr))
 #define __va(paddr)            ((void *)((unsigned long)(paddr)))
 
diff --git a/arch/s390/include/asm/page.h b/arch/s390/include/asm/page.h
index 56da819a79e6..e995d2a413f9 100644
--- a/arch/s390/include/asm/page.h
+++ b/arch/s390/include/asm/page.h
@@ -67,9 +67,6 @@ static inline void copy_page(void *to, void *from)
 
 #define copy_user_page(to, from, vaddr, pg)    copy_page(to, from)
 
-#define vma_alloc_zeroed_movable_folio(vma, vaddr) \
-       vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO, 0, vma, vaddr)
-
 #ifdef CONFIG_STRICT_MM_TYPECHECKS
 #define STRICT_MM_TYPECHECKS
 #endif
diff --git a/arch/x86/include/asm/page.h b/arch/x86/include/asm/page.h
index 416dc88e35c1..92fa975b46f3 100644
--- a/arch/x86/include/asm/page.h
+++ b/arch/x86/include/asm/page.h
@@ -28,9 +28,6 @@ static inline void copy_user_page(void *to, void *from, unsigned long vaddr,
        copy_page(to, from);
 }
 
-#define vma_alloc_zeroed_movable_folio(vma, vaddr) \
-       vma_alloc_folio(GFP_HIGHUSER_MOVABLE | __GFP_ZERO, 0, vma, vaddr)
-
 #ifndef __pa
 #define __pa(x)                __phys_addr((unsigned long)(x))
 #endif


-- 
Cheers,

David