highmem: Add folio_release_kmap()

This is the folio equivalent of unmap_and_put_page(), which remains as
a wrapper for it.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <20230921200746.3303942-1-willy@infradead.org>

Author: Matthew Wilcox (Oracle)

include/linux/highmem.h

@@ -551,10 +551,24 @@ static inline void folio_zero_range(struct folio *folio,
 	zero_user_segments(&folio->page, start, start + length, 0, 0);
 }
 
-static inline void unmap_and_put_page(struct page *page, void *addr)
+/**
+ * folio_release_kmap - Unmap a folio and drop a refcount.
+ * @folio: The folio to release.
+ * @addr: The address previously returned by a call to kmap_local_folio().
+ *
+ * It is common, eg in directory handling to kmap a folio.  This function
+ * unmaps the folio and drops the refcount that was being held to keep the
+ * folio alive while we accessed it.
+ */
+static inline void folio_release_kmap(struct folio *folio, void *addr)
 {
 	kunmap_local(addr);
-	put_page(page);
+	folio_put(folio);
+}
+
+static inline void unmap_and_put_page(struct page *page, void *addr)
+{
+	folio_release_kmap(page_folio(page), addr);
 }
 
 #endif /* _LINUX_HIGHMEM_H */