[Bugfix] Limit the default value of max_model_len when it is not specified by users (#27556)

Signed-off-by: shen-shanshan <467638484@qq.com>

vllm/platforms/interface.py

@@ -608,6 +608,13 @@ class Platform:
         """
         return None
 
+    @classmethod
+    def check_max_model_len(cls, max_model_len: int) -> int:
+        """
+        Check max_model_len for the current platform.
+        """
+        return max_model_len
+
 
 class UnspecifiedPlatform(Platform):
     _enum = PlatformEnum.UNSPECIFIED

vllm/platforms/tpu.py

@@ -251,6 +251,22 @@ class TpuPlatform(Platform):
     def use_sync_weight_loader(cls) -> bool:
         return True
 
+    @classmethod
+    def check_max_model_len(cls, max_model_len: int) -> int:
+        """
+        Check max_model_len for the current platform.
+        """
+        logger.warning(
+            "--max-model-len is not specified, "
+            "it's currently using model's default length %d, "
+            "which might be too large."
+            "Please input with --max-model-len based on your "
+            "request input length and output length, to avoid "
+            "unnecessary degradation.",
+            max_model_len,
+        )
+        return max_model_len
+
 
 try:
     from tpu_inference.platforms import TpuPlatform as TpuInferencePlatform