Re: [PATCH v2 17/33] mm: introduce and use linear_page_delta()

[Vlastimil Babka (SUSE)]

On 7/10/26 22:16, Lorenzo Stoakes wrote:
> It's often useful to obtain the number of pages a given address lies at
> within a VMA.
> 
> Add linear_page_delta() to determine this and update linear_page_index() to
> make use of it.
> 
> Add comments to describe both linear_page_delta() and linear_page_index().
> 
> We refer the reader to the comment for vma_start_pgoff() so we don't
> duplicate information about the meaning of a VMA's page offset, which is
> also less likely to result in bitrot.
> 
> No functional change intended.
> 
> Reviewed-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
> Reviewed-by: Gregory Price <gourry@xxxxxxxxxx>
> Reviewed-by: Pedro Falcato <pfalcato@xxxxxxx>
> Signed-off-by: Lorenzo Stoakes <ljs@xxxxxxxxxx>

Reviewed-by: Vlastimil Babka (SUSE) <vbabka@xxxxxxxxxx>

> ---
>  include/linux/pagemap.h | 33 +++++++++++++++++++++++++++++++--
>  1 file changed, 31 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 2c3718d592d6..a950070b045f 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -1063,11 +1063,40 @@ static inline pgoff_t folio_pgoff(const struct folio *folio)
>  	return folio->index;
>  }
>  
> +/**
> + * linear_page_delta() - Determine the relative page offset of @address within
> + * @vma.
> + * @vma: The VMA in which @address resides.
> + * @address: The address whose relative page offset is required.
> + *
> + * The result is identical for both file-backed and anonymous mappings and
> + * simply determines how many pages @address lies from @vma->vm_start.
> + *
> + * Returns: The number of pages @address is offset by within @vma.
> + */
> +static inline pgoff_t linear_page_delta(const struct vm_area_struct *vma,
> +					const unsigned long address)
> +{
> +	return (address - vma->vm_start) >> PAGE_SHIFT;
> +}
> +
> +/**
> + * linear_page_index() - Determine the absolute page offset of @address within
> + * @vma.
> + * @vma: The VMA in which @address resides.
> + * @address: The address whose absolute page offset is required.
> + *
> + * See the comment for vma_start_pgoff() for a description of what the page
> + * offset signifies.
> + *
> + * Returns: The absolute page offset of @address within @vma.
> + */
>  static inline pgoff_t linear_page_index(const struct vm_area_struct *vma,
>  					const unsigned long address)
>  {
>  	pgoff_t pgoff;
> -	pgoff = (address - vma->vm_start) >> PAGE_SHIFT;
> +
> +	pgoff = linear_page_delta(vma, address);
>  	pgoff += vma->vm_pgoff;
>  	return pgoff;
>  }
> @@ -1219,7 +1248,7 @@ static inline vm_fault_t folio_lock_or_retry(struct folio *folio,
>  void folio_wait_bit(struct folio *folio, int bit_nr);
>  int folio_wait_bit_killable(struct folio *folio, int bit_nr);
>  
> -/* 
> +/*
>   * Wait for a folio to be unlocked.
>   *
>   * This must be called with the caller "holding" the folio,
>