docstr: If under pipeline parallel setting, replacing the original forward method of huggingface
  to customized forward method, and add this changing to policy.
code: def set_pipeline_forward(
      self, model_cls: nn.Module, new_forward: Callable, policy: Dict
  ) -> None:
      """If under pipeline parallel setting, replacing the original forward method of huggingface
      to customized forward method, and add this changing to policy."""
      if not self.pipeline_stage_manager:
          raise ValueError(
              "set_pipeline_forward method can only be called when pipeline parallel is enabled."
          )
      stage_manager = self.pipeline_stage_manager
      if self.model.__class__.__name__ == "GPTJModel":
          module = self.model
      else:
          module = self.model.transformer
  
      layers_per_stage = Policy.distribute_layers(
          len(module.h), stage_manager.num_stages
      )
      stage_index = Policy.get_stage_index(
          layers_per_stage, stage_manager.stage
      )
      method_replacement = {
          "forward": partial(
              new_forward,
              stage_manager=stage_manager,
              stage_index=stage_index,
              shard_config=self.shard_config,
          )
      }
      self.append_or_create_method_replacement(
          description=method_replacement,
          policy=policy,
          target_key=model_cls,
      )
  
imports: import warnings
  from functools import partial
  from typing import Callable, Dict, List
  from torch import Tensor, nn
  import colossalai.shardformer.layer
  from ..modeling.gptj import GPTJPipelineForwards, get_gptj_flash_attention_forward
  from .base_policy import ModulePolicyDescription, Policy, SubModuleReplacementDescription
label_desc: Use image node_id 6 for calling the GPTJPolicy obj's underlying member method code with example usage: obj.set_pipeline_forward(model_cls, new_forward, policy) without return types