Re: [PATCH v2 3/8] mm: move anon-exclusive batch helper to mm.h

[Dev Jain <dev.jain@arm.com>]

On 01/09/26 11:13 am, Dev Jain wrote:
> In preparation for optimizing large folio unmapping, we need to reuse
> the page_anon_exclusive_batch helper in rmap.c and rmap.h and obey the
> existing use in mprotect.c .
> 
> Therefore, move it from mprotect.c to mm.h. Gate with CONFIG_MMU since
> both rmap and mprotect users are built only for CONFIG_MMU.
> 
> While at it, change start_idx and max_len to unsigned long type for
> future proofing against THP support at >= PUD level. Also shorten
> expected_anon_exclusive -> anon_exclusive.
> 
> Signed-off-by: Dev Jain <dev.jain@arm.com>
> ---
>  include/linux/mm.h | 19 +++++++++++++++++++
>  mm/mprotect.c      | 17 -----------------
>  2 files changed, 19 insertions(+), 17 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index dd09c438fa23e..63da8813bc5df 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -244,6 +244,25 @@ static inline unsigned long folio_page_idx(const struct folio *folio,
>  	return page - &folio->page;
>  }
>  
> +#ifdef CONFIG_MMU
> +/*
> + * Get max length of consecutive PTEs pointing to PageAnonExclusive() pages or
> + * !PageAnonExclusive() pages, starting from start_idx. Caller must enforce
> + * that the PTEs point to consecutive pages of the same anon large folio.
> + */
> +static __always_inline int page_anon_exclusive_batch(unsigned long start_idx,

Sashiko says to make the return value unsigned long here, I'll do that. Now we
have an unfortunate mix of int's in existing callers, but keeping nr_pages
unsigned long everywhere eventually seems like the right thing to do.


> +		unsigned long max_len, struct page *first_page, bool anon_exclusive)
> +{
> +	int idx;
> +
> +	for (idx = start_idx + 1; idx < start_idx + max_len; ++idx) {
> +		if (anon_exclusive != PageAnonExclusive(first_page + idx))
> +			break;
> +	}
> +	return idx - start_idx;
> +}
> +#endif
> +
>  static inline struct folio *lru_to_folio(struct list_head *head)
>  {
>  	return list_entry((head)->prev, struct folio, lru);
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index 2888ee638d872..75c2b1a00eb36 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -138,23 +138,6 @@ static __always_inline void prot_commit_flush_ptes(struct vm_area_struct *vma,
>  		tlb_flush_pte_range(tlb, addr, nr_ptes * PAGE_SIZE);
>  }
>  
> -/*
> - * Get max length of consecutive ptes pointing to PageAnonExclusive() pages or
> - * !PageAnonExclusive() pages, starting from start_idx. Caller must enforce
> - * that the ptes point to consecutive pages of the same anon large folio.
> - */
> -static __always_inline int page_anon_exclusive_batch(int start_idx, int max_len,
> -		struct page *first_page, bool expected_anon_exclusive)
> -{
> -	int idx;
> -
> -	for (idx = start_idx + 1; idx < start_idx + max_len; ++idx) {
> -		if (expected_anon_exclusive != PageAnonExclusive(first_page + idx))
> -			break;
> -	}
> -	return idx - start_idx;
> -}
> -
>  /*
>   * This function is a result of trying our very best to retain the
>   * "avoid the write-fault handler" optimization. In can_change_pte_writable(),