On Tue, Feb 28, 2023 at 09:37:06PM +0000, 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>
> ---
> 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 51b75b89730e..1b1ba3d5100d 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
^ folio ?
> + * 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));
> }
>
> /**
> --
> 2.39.1
>
--
Sincerely yours,
Mike.
