fix(accelerate_ppo_trainer): no resizing when using peft reference

trlx/trainer/accelerate_ppo_trainer.py

@@ -69,13 +69,15 @@ def __init__(self, config: TRLConfig, **kwargs):
 
         # Set up a reference model when hydra heads are not used
         if not hasattr(self.model, "frozen_head") and not self.model.peft_type:
+            # Full Reference Copy
             self.ref_model = self.get_arch(self.config)
             self.ref_model.base_model.resize_token_embeddings(len(self.tokenizer))
             self.ref_model.to(self.accelerator.device)
             self.ref_model.eval()
-        else:
-            # resize hydra heads
+        elif hasattr(self.model, "frozen_head"):
+            # Hydra Reference: Use the frozen base layers and head as the reference model, resize hydra heads
             self.model.frozen_head.resize_token_embeddings(len(self.tokenizer))
+        # TODO: else PEFT Reference, do something?
 
         # Set up the KL controller
         # This helps prevent large divergences in the controller (policy)