[Feature] Add script to split HuggingFace model to the smallest sharded checkpoints (#199)

* add get_small_sharded_hf.py

* fix pre-commit

lmdeploy/lite/apis/get_small_sharded_hf.py

+# Copyright (c) OpenMMLab. All rights reserved.
+import argparse
+import copy
+import json
+import os
+import shutil
+
+import torch
+from mmengine.utils import mkdir_or_exist
+
+
+def parse_args():
+    parser = argparse.ArgumentParser(
+        description='Convert a hugging face model to the smallest sharded one')
+    parser.add_argument('src_dir', help='the directory of the model')
+    parser.add_argument('dst_dir', help='the directory to save the new model')
+    args = parser.parse_args()
+    return args
+
+
+def main():
+    args = parse_args()
+    mkdir_or_exist(args.dst_dir)
+
+    all_files = os.listdir(args.src_dir)
+    for name in all_files:
+        if not name.startswith(('pytorch_model', '.')):
+            src_path = os.path.join(args.src_dir, name)
+            dst_path = os.path.join(args.dst_dir, name)
+            shutil.copy(src_path, dst_path)
+
+    with open(os.path.join(args.src_dir, 'pytorch_model.bin.index.json')) as f:
+        index = json.load(f)
+
+    n_shard = len(index['weight_map'])
+    new_index = copy.deepcopy(index)
+    new_index['weight_map'] = {}
+    cnt = 1
+
+    checkpoints = set(index['weight_map'].values())
+    for ckpt in checkpoints:
+        state_dict = torch.load(os.path.join(args.src_dir, ckpt),
+                                map_location='cuda')
+        keys = sorted(list(state_dict.keys()))
+        for k in keys:
+            new_state_dict_name = 'pytorch_model-{:05d}-of-{:05d}.bin'.format(
+                cnt, n_shard)
+            new_index['weight_map'][k] = new_state_dict_name
+            new_state_dict = {k: state_dict[k]}
+            torch.save(new_state_dict,
+                       os.path.join(args.dst_dir, new_state_dict_name))
+            cnt += 1
+        del state_dict
+        torch.cuda.empty_cache()
+    with open(os.path.join(args.dst_dir, 'pytorch_model.bin.index.json'),
+              'w') as f:
+        json.dump(new_index, f)
+    assert new_index['weight_map'].keys() == index['weight_map'].keys(
+    ), 'Mismatch on `weight_map`!'
+
+
+if __name__ == '__main__':
+    main()