Re: [PATCH RFC 09/17] userfaultfd: introduce vm_uffd_ops->alloc_folio()

[Peter Xu <peterx@redhat.com>]

On Tue, Jan 27, 2026 at 09:29:28PM +0200, Mike Rapoport wrote:

[...]

> -static int mfill_atomic_pte_zeroed_folio(pmd_t *dst_pmd,
> -					 struct vm_area_struct *dst_vma,
> -					 unsigned long dst_addr)
> +static int mfill_atomic_pte_copy(struct mfill_state *state)
>  {
> -	struct folio *folio;
> -	int ret = -ENOMEM;
> -
> -	folio = vma_alloc_zeroed_movable_folio(dst_vma, dst_addr);
> -	if (!folio)
> -		return ret;
> -
> -	if (mem_cgroup_charge(folio, dst_vma->vm_mm, GFP_KERNEL))
> -		goto out_put;
> +	const struct vm_uffd_ops *ops = vma_uffd_ops(state->vma);
>  
> -	/*
> -	 * The memory barrier inside __folio_mark_uptodate makes sure that
> -	 * zeroing out the folio become visible before mapping the page
> -	 * using set_pte_at(). See do_anonymous_page().
> -	 */
> -	__folio_mark_uptodate(folio);
> +	return __mfill_atomic_pte(state, ops);
> +}
>  
> -	ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr,
> -				       &folio->page, true, 0);
> -	if (ret)
> -		goto out_put;
> +static int mfill_atomic_pte_zeroed_folio(struct mfill_state *state)
> +{
> +	const struct vm_uffd_ops *ops = vma_uffd_ops(state->vma);
>  
> -	return 0;
> -out_put:
> -	folio_put(folio);
> -	return ret;
> +	return __mfill_atomic_pte(state, ops);
>  }
>  
>  static int mfill_atomic_pte_zeropage(struct mfill_state *state)
> @@ -542,7 +546,7 @@ static int mfill_atomic_pte_zeropage(struct mfill_state *state)
>  	int ret;
>  
>  	if (mm_forbids_zeropage(dst_vma->vm_mm))
> -		return mfill_atomic_pte_zeroed_folio(dst_pmd, dst_vma, dst_addr);
> +		return mfill_atomic_pte_zeroed_folio(state);

After this patch, mfill_atomic_pte_zeroed_folio() should be 100% the same
impl with mfill_atomic_pte_copy(), so IIUC we can drop it.

>  
>  	_dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
>  					 dst_vma->vm_page_prot));
> -- 
> 2.51.0
> 

-- 
Peter Xu