bt_freelist
LIST_FOREACH(bt, list, bt_freelist) {
LIST_FOREACH(bt, fl, bt_freelist) {
LIST_INSERT_HEAD(&vm->vm_freetags, bt, bt_freelist);
LIST_REMOVE(bt, bt_freelist);
LIST_REMOVE(bt, bt_freelist);
LIST_INSERT_HEAD(&freetags, bt, bt_freelist);
LIST_REMOVE(bt, bt_freelist);
LIST_INSERT_HEAD(&vm->vm_freetags, bt, bt_freelist);
LIST_REMOVE(bt, bt_freelist);
LIST_INSERT_HEAD(list, bt, bt_freelist);