Re: [PATCH v4 03/36] mm: Add folio_flush_mapping()

[Anshuman Khandual]

On 3/15/23 10:44, Matthew Wilcox (Oracle) wrote:
> This is the folio equivalent of page_mapping_file(), but rename it
> to make it clear that it's very different from page_file_mapping().
> Theoretically, there's nothing flush-only about it, but there are no
> other users today, and I doubt there will be; it's almost always more
> useful to know the swapfile's mapping or the swapcache's mapping.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>

Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>

> ---
>  include/linux/pagemap.h | 26 +++++++++++++++++++++-----
>  1 file changed, 21 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index a56308a9d1a4..e56c2023aa0e 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -369,6 +369,26 @@ static inline struct address_space *folio_file_mapping(struct folio *folio)
>  	return folio->mapping;
>  }
>  
> +/**
> + * folio_flush_mapping - Find the file mapping this folio belongs to.
> + * @folio: The folio.
> + *
> + * For folios which are in the page cache, return the mapping that this
> + * page belongs to.  Anonymous folios return NULL, even if they're in
> + * the swap cache.  Other kinds of folio also return NULL.
> + *
> + * This is ONLY used by architecture cache flushing code.  If you aren't
> + * writing cache flushing code, you want either folio_mapping() or
> + * folio_file_mapping().
> + */
> +static inline struct address_space *folio_flush_mapping(struct folio *folio)
> +{
> +	if (unlikely(folio_test_swapcache(folio)))
> +		return NULL;
> +
> +	return folio_mapping(folio);
> +}
> +
>  static inline struct address_space *page_file_mapping(struct page *page)
>  {
>  	return folio_file_mapping(page_folio(page));
> @@ -379,11 +399,7 @@ static inline struct address_space *page_file_mapping(struct page *page)
>   */
>  static inline struct address_space *page_mapping_file(struct page *page)
>  {
> -	struct folio *folio = page_folio(page);
> -
> -	if (unlikely(folio_test_swapcache(folio)))
> -		return NULL;
> -	return folio_mapping(folio);
> +	return folio_flush_mapping(page_folio(page));
>  }
>  
>  /**