[PATCH 3/7] mm: Add folio_flush_mapping()

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

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@infradead.org>
---
 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..647c5a036a97 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 swapcache_mapping(folio);
+
+	return folio->mapping;
+}
+
 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