UVM_VNODE_CANPERSIST
uvn->u_flags &= ~UVM_VNODE_CANPERSIST;
uvn->u_flags = UVM_VNODE_VALID|UVM_VNODE_CANPERSIST;
if (uvn->u_flags & UVM_VNODE_CANPERSIST) {
UVM_VNODE_WANTED|UVM_VNODE_CANPERSIST);