uvm_map_reserve
if (!uvm_map_reserve(dstmap, len, start,
int uvm_map_reserve(struct vm_map *, vsize_t, vaddr_t, vsize_t,
if (uvm_map_reserve(oldmap, newsize - oldsize, 0, 0, &va,
if (!uvm_map_reserve(newmap, newsize, oldva, align, &dstva,