Add Mirror Option for Downloads (#6679)

* Add Tuna Mirror for Downloads from China

* format fix

* Use preset instead of hardcoding URL

* Fix

* make style

* update the mirror option doc

* update the mirror

src/transformers/modeling_utils.py

@@ -784,6 +784,10 @@ class PreTrainedModel(nn.Module, ModuleUtilsMixin, GenerationMixin):
             use_cdn(:obj:`bool`, `optional`, defaults to :obj:`True`):
                 Whether or not to use Cloudfront (a Content Delivery Network, or CDN) when searching for the model on
                 our S3 (faster). Should be set to :obj:`False` for checkpoints larger than 20GB.
+            mirror(:obj:`str`, `optional`, defaults to :obj:`None`):
+                Mirror source to accelerate downloads in China. If you are from China and have an accessibility problem,
+                you can set this option to resolve it. Note that we do not guarantee the timeliness or safety. Please
+                refer to the mirror site for more information.
             kwargs (remaining dictionary of keyword arguments, `optional`):
                 Can be used to update the configuration object (after it being loaded) and initiate the model (e.g.,
                 :obj:`output_attentions=True`). Behaves differently depending on whether a ``config`` is provided or
@@ -822,6 +826,7 @@ class PreTrainedModel(nn.Module, ModuleUtilsMixin, GenerationMixin):
         output_loading_info = kwargs.pop("output_loading_info", False)
         local_files_only = kwargs.pop("local_files_only", False)
         use_cdn = kwargs.pop("use_cdn", True)
+        mirror = kwargs.pop("mirror", None)
 
         # Load config if we don't provide a configuration
         if not isinstance(config, PretrainedConfig):
@@ -873,6 +878,7 @@ class PreTrainedModel(nn.Module, ModuleUtilsMixin, GenerationMixin):
                     pretrained_model_name_or_path,
                     filename=(TF2_WEIGHTS_NAME if from_tf else WEIGHTS_NAME),
                     use_cdn=use_cdn,
+                    mirror=mirror,
                 )
 
             try: