mm/writeback: Add folio_cancel_dirty()

Turn __cancel_dirty_page() into __folio_cancel_dirty() and add wrappers.
Move the prototypes into pagemap.h since this is page cache functionality.
Saves 44 bytes of kernel text in total; 33 bytes from __folio_cancel_dirty
and 11 from two callers of cancel_dirty_page().
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Howells <dhowells@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>

include/linux/mm.h

@@ -2008,13 +2008,6 @@ int redirty_page_for_writepage(struct writeback_control *wbc,
 bool folio_mark_dirty(struct folio *folio);
 bool set_page_dirty(struct page *page);
 int set_page_dirty_lock(struct page *page);
-void __cancel_dirty_page(struct page *page);
-static inline void cancel_dirty_page(struct page *page)
-{
-	/* Avoid atomic ops, locking, etc. when not actually needed. */
-	if (PageDirty(page))
-		__cancel_dirty_page(page);
-}
 int clear_page_dirty_for_io(struct page *page);
 
 int get_cmdline(struct task_struct *task, char *buffer, int buflen);

include/linux/pagemap.h

@@ -785,6 +785,17 @@ static inline void account_page_cleaned(struct page *page,
 {
 	return folio_account_cleaned(page_folio(page), mapping, wb);
 }
+void __folio_cancel_dirty(struct folio *folio);
+static inline void folio_cancel_dirty(struct folio *folio)
+{
+	/* Avoid atomic ops, locking, etc. when not actually needed. */
+	if (folio_test_dirty(folio))
+		__folio_cancel_dirty(folio);
+}
+static inline void cancel_dirty_page(struct page *page)
+{
+	folio_cancel_dirty(page_folio(page));
+}
 
 int __set_page_dirty_nobuffers(struct page *page);
 int __set_page_dirty_no_writeback(struct page *page);

mm/page-writeback.c

@@ -2657,28 +2657,28 @@ EXPORT_SYMBOL(set_page_dirty_lock);
  * page without actually doing it through the VM. Can you say "ext3 is
  * horribly ugly"? Thought you could.
  */
-void __cancel_dirty_page(struct page *page)
+void __folio_cancel_dirty(struct folio *folio)
 {
-	struct address_space *mapping = page_mapping(page);
+	struct address_space *mapping = folio_mapping(folio);
 
 	if (mapping_can_writeback(mapping)) {
 		struct inode *inode = mapping->host;
 		struct bdi_writeback *wb;
 		struct wb_lock_cookie cookie = {};
 
-		lock_page_memcg(page);
+		folio_memcg_lock(folio);
 		wb = unlocked_inode_to_wb_begin(inode, &cookie);
 
-		if (TestClearPageDirty(page))
-			account_page_cleaned(page, mapping, wb);
+		if (folio_test_clear_dirty(folio))
+			folio_account_cleaned(folio, mapping, wb);
 
 		unlocked_inode_to_wb_end(inode, &cookie);
-		unlock_page_memcg(page);
+		folio_memcg_unlock(folio);
 	} else {
-		ClearPageDirty(page);
+		folio_clear_dirty(folio);
 	}
 }
-EXPORT_SYMBOL(__cancel_dirty_page);
+EXPORT_SYMBOL(__folio_cancel_dirty);
 
 /*
  * Clear a page's dirty flag, while caring for dirty memory accounting.