Re: [PATCH] mm/memory: use folio lock/ref helpers in do_swap_page

[Matthew Wilcox <willy@infradead.org>]

On Tue, Jul 21, 2026 at 09:33:47AM +0800, Hongfu Li wrote:
> From: Hongfu Li <lihongfu@kylinos.cn>
> 
> Replace page-level lock/ref operations with their folio equivalents
> in the device_private migration path of do_swap_page().

When I do folio conversions, I like to mention the actual advantage
of the patch.  Here, I'd say something like ...

mm: Use a folio in the softleaf_is_device_private path

Use the folio APIs, replacing four calls to compound_head() with one.



> Introduce a local fault_folio to hold page_folio(vmf->page) to avoid
> repeated page_folio() invocations.
> 
> Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>
> ---
>  mm/memory.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index d5e87624f692..bd27372a1052 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4852,6 +4852,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>  			vmf->page = softleaf_to_page(entry);
>  			ret = remove_device_exclusive_entry(vmf);
>  		} else if (softleaf_is_device_private(entry)) {
> +			struct folio *fault_folio;

You can just use the existing 'folio' variable.

Although this function is far too long (400 lines!  14 function-scope
variables!) so I don't blame you for not noticing that.  Pulling a
do_non_swap_page() out of it might be a kindness.

>  			if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
>  				/*
>  				 * migrate_to_ram is not yet ready to operate
> @@ -4863,6 +4865,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>  			}
>  
>  			vmf->page = softleaf_to_page(entry);
> +			fault_folio = page_folio(vmf->page);
>  			vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
>  					vmf->address, &vmf->ptl);
>  			if (unlikely(!vmf->pte ||
> @@ -4874,15 +4877,15 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>  			 * Get a page reference while we know the page can't be
>  			 * freed.

You should also replace 'page' with 'folio' here.  Pages don't have
refcounts, folios do.