On Mon, 10 Jul 2023 21:43:05 +0100 "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> 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>
> +++ b/include/linux/pagemap.h
> @@ -389,6 +389,26 @@ 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);
> +}
The name makes it sound like it flushes something. Wouldn't
folio_flushable_mapping() be clearer?
> static inline struct address_space *page_file_mapping(struct page *page)
> {
> return folio_file_mapping(page_folio(page));
> @@ -399,11 +419,7 @@ 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));
> }
