add conversion script for checkpoint files before version 1.3.1. (#161)

* add conversion script for older checkpoint files.

* fix format

tools/convert_ckpt.py

@@ -0,0 +1,37 @@
+# Copyright (c) Alibaba, Inc. and its affiliates.
+import argparse
+import os
+import shutil
+
+import torch
+
+
+def convert_single_pth(fullname):
+    filename, ext = os.path.splitext(fullname)
+    checkpoint = torch.load(fullname, map_location='cpu')
+    only_module = 'state_dict' not in checkpoint
+    state_dict = checkpoint if only_module else checkpoint['state_dict']
+    torch.save(state_dict, fullname)
+
+    if not only_module:
+        checkpoint.pop('state_dict')
+    fullname_trainer = filename + '_trainer_state' + ext
+    torch.save(checkpoint, fullname_trainer)
+
+
+# This script is used to split pth files which generated before version 1.3.1 into two files.
+# there is only one argument: --dir, fill the dir contains the pth files inside.
+# NOTE: If you are using this script to convert the checkpoints of GPT3 or other sharding models,
+# please rename the checkpoint filenames after the conversion manually.
+parser = argparse.ArgumentParser()
+parser.add_argument('--dir', help='The dir contains the *.pth files.')
+args = parser.parse_args()
+folder = args.dir
+assert folder
+
+all_files = os.listdir(folder)
+all_files = [file for file in all_files if file.endswith('.pth')]
+for file in all_files:
+    shutil.copy(
+        os.path.join(folder, file), os.path.join(folder, file + '.legacy'))
+    convert_single_pth(os.path.join(folder, file))