[Model] Support Mamba (#6484)

vllm/model_executor/models/interfaces.py

@@ -271,7 +271,7 @@ class HasInnerState(Protocol):
     """
         A flag that indicates this model has inner state.
         Models that has inner state usually need access to the scheduler_config
-        for max_num_seqs ,etc... (Currently only used by Jamba)
+        for max_num_seqs, etc. True for e.g. both Mamba and Jamba.
     """
 
     def __init__(self,
@@ -307,3 +307,46 @@ def has_inner_state(
         return isinstance(model, _HasInnerStateType)
 
     return isinstance(model, HasInnerState)
+
+
+@runtime_checkable
+class IsAttentionFree(Protocol):
+    """The interface required for all models like Mamba that lack attention,
+    but do have state whose size is constant wrt the number of tokens."""
+
+    is_attention_free: ClassVar[Literal[True]] = True
+    """
+        A flag that indicates this model has no attention.
+        Used for block manager and attention backend selection.
+        True for Mamba but not Jamba.
+    """
+
+    def __init__(self) -> None:
+        ...
+
+
+@runtime_checkable
+class _IsAttentionFreeType(Protocol):
+    is_attention_free: ClassVar[Literal[True]]
+
+    def __init__(self) -> None:
+        ...
+
+
+@overload
+def is_attention_free(model: object) -> TypeIs[IsAttentionFree]:
+    ...
+
+
+@overload
+def is_attention_free(model: Type[object]) -> TypeIs[Type[IsAttentionFree]]:
+    ...
+
+
+def is_attention_free(
+    model: Union[Type[object], object]
+) -> Union[TypeIs[Type[IsAttentionFree]], TypeIs[IsAttentionFree]]:
+    if isinstance(model, type):
+        return isinstance(model, _IsAttentionFreeType)
+
+    return isinstance(model, IsAttentionFree)