[trainer] remove --model_parallel (#9451)

* fix bad merge - dropped code

* remove --model_parallel

* Deal with TrainingArguments

* Use a private attr and fix batch sizes

* fix _n_gpu

* add is_parallel helper wrapper

* fix attribute

* introduce a new attribute is_model_parallel

* docs

* docs

* Put back init False and rearrange doc

* Ignore non-init args in HFArgumentParser

Co-authored-by: Sylvain Gugger <sylvain.gugger@gmail.com>

src/transformers/hf_argparser.py

@@ -53,6 +53,8 @@ class HfArgumentParser(ArgumentParser):
 
     def _add_dataclass_arguments(self, dtype: DataClassType):
         for field in dataclasses.fields(dtype):
+            if not field.init:
+                continue
             field_name = f"--{field.name}"
             kwargs = field.metadata.copy()
             # field.metadata is not used at all by Data Classes,
@@ -148,7 +150,7 @@ class HfArgumentParser(ArgumentParser):
         namespace, remaining_args = self.parse_known_args(args=args)
         outputs = []
         for dtype in self.dataclass_types:
-            keys = {f.name for f in dataclasses.fields(dtype)}
+            keys = {f.name for f in dataclasses.fields(dtype) if f.init}
             inputs = {k: v for k, v in vars(namespace).items() if k in keys}
             for k in keys:
                 delattr(namespace, k)