vm: use vm_memory_mode() to determine which model to initialise

vm/bootstrap.c

@@ -22,7 +22,17 @@ kern_status_t vm_bootstrap(const vm_zone_descriptor_t *zones, size_t nr_zones)
 	/* TODO select which memory model to use automatically, and add
 	   a kernel boot parameter to override the choice */
 	vm_set_memory_model(VM_MODEL_SPARSE);
+
+	switch (vm_memory_model()) {
+	case VM_MODEL_SPARSE:
 		vm_sparse_init();
+		break;
+	case VM_MODEL_FLAT:
+		vm_flat_init();
+		break;
+	default:
+		break;
+	}
 
 	for (size_t i = 0; i < nr_zones; i++) {
 		vm_zone_init(&node_data->pg_zones[zones[i].zd_id],  &zones[i]);