if (size == 0) return;
if (map == NULL) panic("uvm_deallocate with null map");
uvm_deallocate(map, start, size)	struct vm_map *map;	vaddr_t start;	vsize_t size;{	if (size == 0)		return;	uvm_unmap(map, trunc_page(start), round_page(start + size));}