Re: [PATCH v2 2/2] mm: Extract non-swap page handling to do_non_swap_page()

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

On Thu, Jul 23, 2026 at 11:07:52AM +0800, Hongfu Li wrote:
> From: Hongfu Li <lihongfu@kylinos.cn>
>
> Factor non-swap entry logic out of bloated do_swap_page() to simplify
> the main swap fault flow and improve readability.
>
> The new do_non_swap_page() handles migration, device private/exclusive,
> hwpoison, marker and bad PTE entries.
>
> Signed-off-by: Hongfu Li <lihongfu@kylinos.cn>

We've already gone over this elsewhere in the thread, we don't want a
do_non_swap_page() (HELL no).

But in general I want to finish what I started with softleaves, which still has
some work to do with swap entries so maybe could you just drop this patch so I
can follow up with that later?

That way you can do a respin of just the 1/2 as a v3.

Thanks, Lorenzo

> ---
>  mm/memory.c | 120 ++++++++++++++++++++++++++++++----------------------
>  1 file changed, 69 insertions(+), 51 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index ae521baa8c84..50d8e92aef91 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4815,6 +4815,74 @@ static void check_swap_exclusive(struct folio *folio, swp_entry_t entry,
>  	} while (--nr_pages);
>  }
>
> +static vm_fault_t do_non_swap_page(struct vm_fault *vmf)
> +{
> +	struct vm_area_struct *vma = vmf->vma;
> +	struct folio *folio;
> +	softleaf_t entry;
> +	vm_fault_t ret = 0;
> +
> +	entry = softleaf_from_pte(vmf->orig_pte);
> +	if (softleaf_is_migration(entry)) {
> +		migration_entry_wait(vma->vm_mm, vmf->pmd,
> +				     vmf->address);
> +	} else if (softleaf_is_device_exclusive(entry)) {
> +		vmf->page = softleaf_to_page(entry);
> +		ret = remove_device_exclusive_entry(vmf);
> +	} else if (softleaf_is_device_private(entry)) {
> +
> +		if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
> +			/*
> +			 * migrate_to_ram is not yet ready to operate
> +			 * under VMA lock.
> +			 */
> +			vma_end_read(vma);
> +			return VM_FAULT_RETRY;
> +		}
> +
> +		vmf->page = softleaf_to_page(entry);
> +		vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
> +						vmf->address, &vmf->ptl);
> +		if (unlikely(!vmf->pte ||
> +			     !pte_same(ptep_get(vmf->pte),
> +					vmf->orig_pte)))
> +			goto unlock;
> +
> +		/*
> +		 * Get a folio reference while we know the folio can't be
> +		 * freed.
> +		 */
> +		folio = page_folio(vmf->page);
> +		if (folio_trylock(folio)) {
> +			struct dev_pagemap *pgmap;
> +
> +			folio_get(folio);
> +			pte_unmap_unlock(vmf->pte, vmf->ptl);
> +			pgmap = page_pgmap(vmf->page);
> +			ret = pgmap->ops->migrate_to_ram(vmf);
> +			folio_unlock(folio);
> +			folio_put(folio);
> +		} else {
> +			pte_unmap(vmf->pte);
> +			softleaf_entry_wait_on_locked(entry, vmf->ptl);
> +		}
> +	} else if (softleaf_is_hwpoison(entry)) {
> +		ret = VM_FAULT_HWPOISON;
> +	} else if (softleaf_is_marker(entry)) {
> +		ret = handle_pte_marker(vmf);
> +	} else {
> +		print_bad_pte(vma, vmf->address, vmf->orig_pte, NULL);
> +		ret = VM_FAULT_SIGBUS;
> +	}
> +
> +	return ret;
> +
> +unlock:
> +	if (vmf->pte)
> +		pte_unmap_unlock(vmf->pte, vmf->ptl);
> +	return ret;
> +}
> +
>  /*
>   * We enter with either the VMA lock or the mmap_lock held (see
>   * FAULT_FLAG_VMA_LOCK), and pte mapped but not yet locked.
> @@ -4845,57 +4913,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>
>  	entry = softleaf_from_pte(vmf->orig_pte);
>  	if (unlikely(!softleaf_is_swap(entry))) {
> -		if (softleaf_is_migration(entry)) {
> -			migration_entry_wait(vma->vm_mm, vmf->pmd,
> -					     vmf->address);
> -		} else if (softleaf_is_device_exclusive(entry)) {
> -			vmf->page = softleaf_to_page(entry);
> -			ret = remove_device_exclusive_entry(vmf);
> -		} else if (softleaf_is_device_private(entry)) {
> -			if (vmf->flags & FAULT_FLAG_VMA_LOCK) {
> -				/*
> -				 * migrate_to_ram is not yet ready to operate
> -				 * under VMA lock.
> -				 */
> -				vma_end_read(vma);
> -				ret = VM_FAULT_RETRY;
> -				goto out;
> -			}
> -
> -			vmf->page = softleaf_to_page(entry);
> -			vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
> -					vmf->address, &vmf->ptl);
> -			if (unlikely(!vmf->pte ||
> -				     !pte_same(ptep_get(vmf->pte),
> -							vmf->orig_pte)))
> -				goto unlock;
> -
> -			/*
> -			 * Get a folio reference while we know the folio can't be
> -			 * freed.
> -			 */
> -			folio = page_folio(vmf->page);
> -			if (folio_trylock(folio)) {
> -				struct dev_pagemap *pgmap;
> -
> -				folio_get(folio);
> -				pte_unmap_unlock(vmf->pte, vmf->ptl);
> -				pgmap = page_pgmap(vmf->page);
> -				ret = pgmap->ops->migrate_to_ram(vmf);
> -				folio_unlock(folio);
> -				folio_put(folio);
> -			} else {
> -				pte_unmap(vmf->pte);
> -				softleaf_entry_wait_on_locked(entry, vmf->ptl);
> -			}
> -		} else if (softleaf_is_hwpoison(entry)) {
> -			ret = VM_FAULT_HWPOISON;
> -		} else if (softleaf_is_marker(entry)) {
> -			ret = handle_pte_marker(vmf);
> -		} else {
> -			print_bad_pte(vma, vmf->address, vmf->orig_pte, NULL);
> -			ret = VM_FAULT_SIGBUS;
> -		}
> +		ret = do_non_swap_page(vmf);
>  		goto out;
>  	}
>
> --
> 2.54.0
>