[model] Reduce medusa weight (#10454)

Signed-off-by: skylee-01 <[email protected]>

Author: skylee-01

vllm/model_executor/models/medusa.py

@@ -61,14 +61,25 @@ def __init__(self, *, vllm_config: VllmConfig, prefix: str = "") -> None:
         self.truncated_vocab_size = config.truncated_vocab_size
         self.unpadded_vocab_size = self.truncated_vocab_size
 
-        self.lm_heads = nn.ModuleList([
-            ParallelLMHead(
+        if getattr(config, "original_lm_head", False):
+            self.lm_head = ParallelLMHead(
                 self.unpadded_vocab_size,
                 config.hidden_size,
                 org_num_embeddings=self.truncated_vocab_size,
                 padding_size=DEFAULT_VOCAB_PADDING_SIZE,
-            ) for _ in range(self.config.num_heads)
-        ])
+            )
+            self.lm_heads = [
+                self.lm_head for _ in range(self.config.num_heads)
+            ]
+        else:
+            self.lm_heads = nn.ModuleList([
+                ParallelLMHead(
+                    self.unpadded_vocab_size,
+                    config.hidden_size,
+                    org_num_embeddings=self.truncated_vocab_size,
+                    padding_size=DEFAULT_VOCAB_PADDING_SIZE,
+                ) for _ in range(self.config.num_heads)
+            ])
 
         logit_scale = getattr(config, "logit_scale", 1.0)
         self.logits_processor = LogitsProcessor(self.unpadded_vocab_size,
@@ -172,6 +183,9 @@ def load_weights(self, weights: Iterable[Tuple[str,
                                                   requires_grad=False)
             elif name in params_dict:
                 weights_map[name] = loaded_weight
+            elif (getattr(self.config, "original_lm_head", False)
+                  and name == "lm_heads.0.weight"):
+                weights_map["lm_head.weight"] = loaded_weight
 
         for name, loaded_weight in weights_map.items():
             if "lm_head" in name and self.token_map is not None and\