nilfs2: convert nilfs_mdt_write_page() 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/20231114084436.2755-8-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/mdt.c

@@ -399,7 +399,8 @@ int nilfs_mdt_fetch_dirty(struct inode *inode)
 static int
 nilfs_mdt_write_page(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;
 	struct super_block *sb;
 	int err = 0;
 
@@ -407,16 +408,16 @@ nilfs_mdt_write_page(struct page *page, struct writeback_control *wbc)
 		/*
 		 * It means that filesystem was remounted in read-only
 		 * mode because of error or metadata corruption. But we
-		 * have dirty pages that try to be flushed in background.
-		 * So, here we simply discard this dirty page.
+		 * have dirty folios that try to be flushed in background.
+		 * So, here we simply discard this dirty folio.
 		 */
 		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 (!inode)
 		return 0;