feat: enable trl's autounwrap (#1060)

* feat: test trl's autounwrap

* fix: add check for adapter

* feat: add config to disable autounwrap

* chore: fix lint

docs/rlhf.md

@@ -33,3 +33,12 @@ datasets:
 ```yaml
 rl: ipo
 ```
+
+#### Trl autounwrap for peft
+
+Trl supports autounwrapping peft models, so that a ref model does not need to be additionally loaded, leading to less VRAM needed. This is on by default. To turn it off, pass the following config.
+
+```yaml
+# load ref model when adapter training.
+rl_adapter_ref_model: true
+```

src/axolotl/train.py

@@ -63,10 +63,15 @@ def train(
     model, peft_config = load_model(cfg, tokenizer, inference=cli_args.inference)
     model_ref = None
     if cfg.rl:
-        # load the model again for model_ref/baseline
-        model_ref, _ = load_model(
-            cfg, tokenizer, inference=cli_args.inference, reference_model=True
-        )
+        if cfg.adapter and not cfg.rl_adapter_ref_model:
+            # use built-in trl autounwrap
+            LOG.debug("Passing model_ref: None to RL trainer")
+            model_ref = None  # explicit setting to None
+        else:
+            # load the model again for model_ref/baseline
+            model_ref, _ = load_model(
+                cfg, tokenizer, inference=cli_args.inference, reference_model=True
+            )
 
     safe_serialization = cfg.save_safetensors is True