nilfs2: convert nilfs_writepage() to use a folio

Convert the incoming page to a folio.  Replaces three calls to
compound_head() with one.

Link: https://lkml.kernel.org/r/20231114084436.2755-7-konishi.ryusuke@gmail.comSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/nilfs2/inode.c

@@ -175,7 +175,8 @@ static int nilfs_writepages(struct address_space *mapping,
 
 static int nilfs_writepage(struct page *page, struct writeback_control *wbc)
 {
-	struct inode *inode = page->mapping->host;
+	struct folio *folio = page_folio(page);
+	struct inode *inode = folio->mapping->host;
 	int err;
 
 	if (sb_rdonly(inode->i_sb)) {
@@ -186,12 +187,12 @@ static int nilfs_writepage(struct page *page, struct writeback_control *wbc)
 		 * So, here we simply discard this dirty page.
 		 */
 		nilfs_clear_dirty_page(page, false);
-		unlock_page(page);
+		folio_unlock(folio);
 		return -EROFS;
 	}
 
-	redirty_page_for_writepage(wbc, page);
-	unlock_page(page);
+	folio_redirty_for_writepage(wbc, folio);
+	folio_unlock(folio);
 
 	if (wbc->sync_mode == WB_SYNC_ALL) {
 		err = nilfs_construct_segment(inode->i_sb);