Re: [PATCH 2/8] mm/khugepaged: extract young page check into collapse_is_young() helper

[Usama Arif <usama.arif@linux.dev>]

On Mon,  6 Jul 2026 09:44:49 -0600 Nico Pache <npache@redhat.com> wrote:

> The change deduplicates the "is this PTE young enough to count as
> referenced" 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.
> 
> Signed-off-by: Nico Pache <npache@redhat.com>

Acked-by: Usama Arif <usama.arif@linux.dev>


> ---
>  mm/khugepaged.c | 35 +++++++++++++++++++----------------
>  1 file changed, 19 insertions(+), 16 deletions(-)
> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index b3985b854e77..48b008a3c891 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -675,6 +675,23 @@ static void release_pte_pages(pte_t *pte, pte_t *_pte,
>  	}
>  }
>  
> +/*
> + * collapse_is_young() - Check for enough young pte to justify collapsing
> + *
> + * If collapse was initiated by khugepaged, check that the page has been
> + * recently accessed (young pte) to justify collapsing the page.
> + *
> + * Return: true if the page has been recently accessed (young pte).
> + */
> +static inline bool collapse_is_young(struct collapse_control *cc, pte_t pteval,
> +	struct folio *folio, struct vm_area_struct *vma, unsigned long addr)
> +{
> +	return cc->is_khugepaged &&
> +	       (pte_young(pteval) || folio_test_young(folio) ||
> +		folio_test_referenced(folio) ||
> +		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)
> @@ -813,14 +830,7 @@ 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)))
> +		if (collapse_is_young(cc, pteval, folio, vma, addr))
>  			referenced++;
>  	}
>  
> @@ -1769,14 +1779,7 @@ 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)))
> +		if (collapse_is_young(cc, pteval, folio, vma, addr))
>  			referenced++;
>  	}
>  	if (cc->is_khugepaged &&
> -- 
> 2.54.0
> 
>