Re: [PATCH v4 2/7] mm/khugepaged: extract reference check into folio_pte_referenced() helper

[Lorenzo Stoakes (ARM)]

On Tue, Aug 11, 2026 at 06:48:34AM -0600, Nico Pache (Red Hat) wrote:
> This change deduplicates the "is this PTE/folio referenced enough to be
> considered for a collapse" condition that was repeated in both
> __collapse_huge_page_isolate() and collapse_scan_pmd(), extracting it into
> a single inline helper function.
>
> Also move the comment and use it as the function header. While we are at
> it, updated the comment to clarify that a young pte is a recently accessed
> one.
>
> Acked-by: Usama Arif <usama.arif@xxxxxxxxx>
> Signed-off-by: Nico Pache (Red Hat) <nico.pache@xxxxxxxxx>

With below addressed nice cleanup so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>

> ---
>  mm/khugepaged.c | 32 ++++++++++++++++++--------------
>  1 file changed, 18 insertions(+), 14 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 1e26ea97381a..8babd4c97db6 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -672,6 +672,22 @@ static void release_pte_pages(pte_t *pte, pte_t *_pte,
>  	}
>  }
>
> +/*
> + * folio_pte_referenced() - Check if a folio or its PTE mapping was recently used
> + *
> + * Return: true if recent access was observed through either the folio state
> + * or the current PTE mapping.
> + */

As discussed please drop :)

> +static inline bool folio_pte_referenced(struct folio *folio,

Please remove inline, for any sane compiler (i.e. any we reasonably support)
this makes no difference for a static function within a compilation unit.

> +		struct vm_area_struct *vma, unsigned long addr, pte_t pteval)
> +{
> +	/* The folio was referenced previously ... */
> +	if (folio_test_young(folio) || folio_test_referenced(folio))
> +		return true;
> +	/* ... or the PTE mapping was recently used */
> +	return pte_young(pteval) || mmu_notifier_test_young(vma->vm_mm, addr);
> +}
> +
>  static enum scan_result __collapse_huge_page_isolate(struct vm_area_struct *vma,
>  		unsigned long start_addr, pte_t *pte, struct collapse_control *cc,
>  		unsigned int order, struct list_head *compound_pagelist)
> @@ -810,14 +826,8 @@ static enum scan_result __collapse_huge_page_isolate(struct vm_area_struct *vma,
>  		if (folio_test_large(folio))
>  			list_add_tail(&folio->lru, compound_pagelist);
>  next:
> -		/*
> -		 * If collapse was initiated by khugepaged, check that there is
> -		 * enough young pte to justify collapsing the page
> -		 */
>  		if (cc->is_khugepaged &&
> -		    (pte_young(pteval) || folio_test_young(folio) ||
> -		     folio_test_referenced(folio) ||
> -		     mmu_notifier_test_young(vma->vm_mm, addr)))
> +		    folio_pte_referenced(folio, vma, addr, pteval))
>  			referenced++;
>  	}
>
> @@ -1766,14 +1776,8 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm,
>  			goto out_unmap;
>  		}
>
> -		/*
> -		 * If collapse was initiated by khugepaged, check that there is
> -		 * enough young pte to justify collapsing the page
> -		 */
>  		if (cc->is_khugepaged &&
> -		    (pte_young(pteval) || folio_test_young(folio) ||
> -		     folio_test_referenced(folio) ||
> -		     mmu_notifier_test_young(vma->vm_mm, addr)))
> +		    folio_pte_referenced(folio, vma, addr, pteval))
>  			referenced++;
>  	}
>  	if (cc->is_khugepaged &&
>
> --
> 2.55.0
>

--
Cheers, Lorenzo