Fix TrainingArguments regression with torch <2.0.0 for dataloader_prefetch_factor (#29447)

* Fix TrainingArguments regression with torch <2.0.0 for dataloader_prefetch_factor

dataloader_prefetch_factor was added to TrainingArguments in #28498 with the default value None, but  versions of torch<2.0.0 do not accept None and will raise an error if num_workers == 0 and prefetch_factor != 2

* Add is_torch_available() check

* Use is_torch_greater_or_equal_than_2_0

add back check for dataloader_prefetch_factor

src/transformers/training_args.py

@@ -66,6 +66,8 @@ if is_torch_available():
     import torch
     import torch.distributed as dist
 
+    from .pytorch_utils import is_torch_greater_or_equal_than_2_0
+
 if is_accelerate_available():
     from accelerate.state import AcceleratorState, PartialState
     from accelerate.utils import DistributedType
@@ -1023,13 +1025,13 @@ class TrainingArguments:
             )
         },
     )
-    dataloader_prefetch_factor: int = field(
-        default=None,
+    dataloader_prefetch_factor: Optional[int] = field(
+        default=None if not is_torch_available() or is_torch_greater_or_equal_than_2_0 else 2,
         metadata={
             "help": (
                 "Number of batches loaded in advance by each worker. "
                 "2 means there will be a total of 2 * num_workers batches prefetched across all workers. "
-                "Default is unset"
+                "Default is 2 for PyTorch < 2.0.0 and otherwise None."
             )
         },
     )
@@ -1807,7 +1809,11 @@ class TrainingArguments:
         if self.use_cpu:
             self.dataloader_pin_memory = False
 
-        if self.dataloader_num_workers == 0 and self.dataloader_prefetch_factor is not None:
+        if (
+            (not is_torch_available() or is_torch_greater_or_equal_than_2_0)
+            and self.dataloader_num_workers == 0
+            and self.dataloader_prefetch_factor is not None
+        ):
             raise ValueError(
                 "--dataloader_prefetch_factor can only be set when data is loaded in a different process, i.e."
                 " when --dataloader_num_workers > 1."