Index: kernel/generic/src/mm/backend_phys.c
===================================================================
--- kernel/generic/src/mm/backend_phys.c	(revision aafed151536405cdb1390b88b7e4ac7c285dd53e)
+++ kernel/generic/src/mm/backend_phys.c	(revision 2cc569a32f7a224374397a5bf949d29b469490ca)
@@ -143,5 +143,5 @@
 	    as_area_get_flags(area));
 
-	if (!used_space_insert(area, upage, 1))
+	if (!used_space_insert(&area->used_space, upage, 1))
 		panic("Cannot insert used space.");