Flax Remat for LongT5 (#17994)

* [Flax] Add remat (gradient checkpointing)

* fix variable naming in test

* flip: checkpoint using a method

* fix naming

* fix class naming

* apply PVP's suggestions from code review

* add gradient_checkpointing to examples

* Add gradient_checkpointing to run_mlm_flax

* Add remat to longt5

* Add gradient checkpointing test longt5

* Fix args errors

* Fix remaining tests

* Make fixup & quality fixes

* replace kwargs

* remove unecessary kwargs

* Make fixup changes

* revert long_t5_flax changes

* Remove return_dict and copy to LongT5

* Remove test_gradient_checkpointing

Co-authored-by: sanchit-gandhi <sanchit@huggingface.co>

examples/flax/language-modeling/run_mlm_flax.py

@@ -107,6 +107,12 @@ class TrainingArguments:
         default=None, metadata={"help": "The name of the repository to keep in sync with the local `output_dir`."}
     )
     hub_token: str = field(default=None, metadata={"help": "The token to use to push to the Model Hub."})
+    gradient_checkpointing: bool = field(
+        default=False,
+        metadata={
+            "help": "If True, use gradient checkpointing to save memory at the expense of slower backward pass."
+        },
+    )
 
     def __post_init__(self):
         if self.output_dir is not None:
@@ -640,6 +646,9 @@ def main():
             dtype=getattr(jnp, model_args.dtype),
         )
 
+    if training_args.gradient_checkpointing:
+        model.enable_gradient_checkpointing()
+
     # Store some constant
     num_epochs = int(training_args.num_train_epochs)
     train_batch_size = int(training_args.per_device_train_batch_size) * jax.device_count()