接口：https://oneflow.readthedocs.io/en/master/graph.html#oneflow.nn.graph.block_config.BlockConfig.activation_checkpointing 参考的例子： https://github.com/Oneflow-Inc/oneflow/blob/master/python/oneflow/test/graph/test_graph_activation_checkpoint.py 参考背景资料：https://pytorch.org/docs/stable/checkpoint.html
