buffer: use b_folio in mark_buffer_dirty()

Removes about four calls to compound_head().  Two of them are inline which
removes 132 bytes from the kernel text.

Link: https://lkml.kernel.org/r/20221215214402.3522366-8-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/buffer.c

@@ -1095,16 +1095,16 @@ void mark_buffer_dirty(struct buffer_head *bh)
 	}
 
 	if (!test_set_buffer_dirty(bh)) {
-		struct page *page = bh->b_page;
+		struct folio *folio = bh->b_folio;
 		struct address_space *mapping = NULL;
 
-		lock_page_memcg(page);
-		if (!TestSetPageDirty(page)) {
-			mapping = page_mapping(page);
+		folio_memcg_lock(folio);
+		if (!folio_test_set_dirty(folio)) {
+			mapping = folio->mapping;
 			if (mapping)
-				__set_page_dirty(page, mapping, 0);
+				__folio_mark_dirty(folio, mapping, 0);
 		}
-		unlock_page_memcg(page);
+		folio_memcg_unlock(folio);
 		if (mapping)
 			__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
 	}