code: def clear(self):
      self.unreleased_grad_flag.clear()
      self.unreleased_grad_volume = 0
  
imports: from contextlib import contextmanager
  from enum import Enum
  from functools import partial
  from typing import List
  import torch
  from colossalai.legacy.zero.gemini.tensor_utils import alloc_storage, free_storage
  from colossalai.tensor.param_op_hook import ColoParamOpHook
  from colossalai.zero.gemini.memory_tracer import MemStats, SyncCudaMemoryMonitor
label_desc: Use image node_id 2 for calling the GradMemStats obj's underlying member method code with example usage: obj.clear() without return types