Fix head_size in NeMo to HF checkpoint converters for width pruned model support
You need to signoff commit: `git commit -s -m "MESSAGE"` else NeMo wont allow: https://github.com/NVIDIA/NeMo/pull/11230/checks?check_run_id=32714934933 FYI) @kevalmorabia97 
When I add args related to tokenizer, I encounter errors as below.

I put manually modified config file to `hf_input_path` and got converted ckpt into the same path (`--hf_output_path`). 

- Script
````
python /opt/NeMo/scripts/checkpoint_converters/convert_llama_nemo_to_hf.py \
    --input_name_or_path ${base_dir}/KD/distill_trainings/megatron_llama_distill/checkpoints/distilled_4b_model_extracted \
    --output_path ${base_dir}/ckpt/distilled_4b_model_llama3_8b_inst/pytorch_model.bin \
    --hf_input_path ${base_dir}/ckpt/distilled_4b_model_llama3_8b_inst \
    --hf_output_path ${base_dir}/ckpt/distilled_4b_model_llama3_8b_inst
````

- Error msg

```
converting layer 31
done layer 31
[NeMo I 2024-11-08 13:34:37 convert_llama_nemo_to_hf:228] Weights saved to /<base_dir>/ckpt/distilled_4b_model_llama3_8b_inst/pytorch_model.bin
Loading checkpoint shards: 100%|██████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 2/2 [00:00<00:00,  3.55it/s]
The tokenizer class you load from this checkpoint is not the same type as the class this function is called from. It may result in unexpected tokenization. 
The tokenizer class you load from this checkpoint is 'PreTrainedTokenizerFast'. 
The class this function is called from is 'LlamaTokenizer'.
[rank0]: Traceback (most recent call last):
[rank0]:   File "/opt/NeMo/scripts/checkpoint_converters/convert_llama_nemo_to_hf.py", line 275, in <module>
[rank0]:     replace_hf_weights_and_tokenizer(
[rank0]:   File "/opt/NeMo/scripts/checkpoint_converters/convert_llama_nemo_to_hf.py", line 249, in replace_hf_weights_and_tokenizer
[rank0]:     tokenizer = LlamaTokenizer.from_pretrained(
[rank0]:   File "/usr/local/lib/python3.10/dist-packages/transformers/tokenization_utils_base.py", line 2213, in from_pretrained
[rank0]:     return cls._from_pretrained(
[rank0]:   File "/usr/local/lib/python3.10/dist-packages/transformers/tokenization_utils_base.py", line 2447, in _from_pretrained
[rank0]:     tokenizer = cls(*init_inputs, **init_kwargs)
[rank0]:   File "/opt/NeMo/nemo/lightning/io/mixin.py", line 577, in wrapped_init
[rank0]:     original_init(self, *args, **kwargs)
[rank0]:   File "/usr/local/lib/python3.10/dist-packages/transformers/models/llama/tokenization_llama.py", line 169, in __init__
[rank0]:     self.sp_model = self.get_spm_processor(kwargs.pop("from_slow", False))
[rank0]:   File "/usr/local/lib/python3.10/dist-packages/transformers/models/llama/tokenization_llama.py", line 199, in get_spm_processor
[rank0]:     with open(self.vocab_file, "rb") as f:
[rank0]: TypeError: expected str, bytes or os.PathLike object, not NoneType
``` Thanks @kevalmorabia97 
I applied sign-off to the commit @cuichenx can you please comment on the tokenizer issue posted above? Does that require some other parameters to be updated to tokenizer loading logic? can you try setting `hf_output_path` to a different dir? > can you try setting `hf_output_path` to a different dir?

@cuichenx 
I gave it a try with a different dir but it didn't work🤔. I got the same error msg

- modified script

````
python /opt/NeMo/scripts/checkpoint_converters/convert_llama_nemo_to_hf.py \
    --input_name_or_path ${base_dir}/KD/distill_trainings/megatron_llama_distill/checkpoints/distilled_4b_model_extracted \
    --output_path ${base_dir}/ckpt/distilled_4b_model_llama3_8b_inst/pytorch_model.bin \
    --hf_input_path ${base_dir}/ckpt/distilled_4b_model_llama3_8b_inst \
    --hf_output_path ${base_dir}/ckpt/distilled_4b_model_llama3_8b_inst_2 \
    --input_tokenizer ${base_dir}/ckpt/Meta-Llama-3-8B-Instruct \
    --hf_output_tokenizer ${base_dir}/ckpt/distilled_4b_model_llama3_8b_inst_2
```` @cuichenx seems like with different output path as well there is the same issue with tokenizer. Can you suggest how to fix that?
Weight conversion works fine and pruning never touches the tokenizer so doesn't seem to be related to ModelOpt Pruning I'm not sure. @tdene added support for the tokenizer. Do you have any idea? Discussed offline. My comments on how to fix the tokenizer-related issue are as follows:

Change the script explanation to
```
"""
Script to convert a llama checkpoint in nemo (mcore path) into a HuggingFace checkpoint.
This script can be used to 1) generate only the HF weights, or 2) generate an entire HF model folder.

1) Generate only HF weights from a nemo file:

    python convert_llama_nemo_to_hf.py \
    --input_name_or_path /path/to/file.nemo or /path/to/extracted_folder \
    --output_path /path/to/pytorch_model.bin
    
2) Generate the full HF model folder

    python convert_llama_nemo_to_hf.py \
    --input_name_or_path /path/to/file.nemo or /path/to/extracted_folder \
    --output_path /path/to/pytorch_model.bin \
    --hf_input_path /path/to/input_hf_folder \
    --hf_output_path /path/to/output_hf_folder

3) Generate the full HF model folder with a custom tokenizer

    python convert_llama_nemo_to_hf.py \
    --input_name_or_path /path/to/file.nemo or /path/to/extracted_folder \
    --output_path /path/to/pytorch_model.bin \
    --hf_input_path /path/to/input_hf_folder \
    --hf_output_path /path/to/output_hf_folder \
    --input_tokenizer /path/to/custom_nemo_tokenizer.model \
    --hf_output_tokenizer /path/to/output_tokenizer

    Use the --cpu-only flag if the model cannot fit in the GPU (e.g. Llama2 70b). 
    However this option makes the conversion script significantly slower.
"""
```

Change L248 through 257 to
```
    if tokenizer_path:
        try:
            tokenizer = LlamaTokenizer.from_pretrained(
                tokenizer_path,
                local_files_only=True,
                legacy=False,
            )
            tmp_tokenizer = convert_slow_tokenizer.convert_slow_tokenizer(tokenizer)
            fast_tokenizer = LlamaTokenizerFast(tokenizer_object=tmp_tokenizer)
            tokenizer_length = len(fast_tokenizer)
            model.resize_token_embeddings(tokenizer_length)
        except:
            tokenizer = None
            logger.warning("Could not load custom tokenizer, proceeding with default tokenizer")
```

Change L263 through 266 to
```
    if tokenizer_path and (tokenizer is not None):
        fast_tokenizer.save_pretrained(output_hf_tokenizer)
        tokenizer.save_pretrained(output_hf_tokenizer)
        logging.info(f"Tokenizer saved to {output_hf_tokenizer}")
```
# What does this PR do ?

- update llama ckpt converter for supporting width pruning. 
  - change head_size as kv_channels
- Because of [width pruning of hidden_size](https://github.com/eagle705/NeMo/blob/main/examples/nlp/language_modeling/megatron_gpt_prune.py#L113), attention head size should be updated by kv_channels.  


# Changelog 
-  update llama ckpt converter's attention head dim size by kv_channels 
- `head_size = model.cfg.get("kv_channels") or (hidden_size // head_num)`

# Usage

```python
    hidden_size = model.cfg.hidden_size
    head_num = model.cfg.num_attention_heads
    num_layers = model.cfg.num_layers
    ffn_hidden_size = model.cfg.ffn_hidden_size
    num_query_groups = model.cfg.get("num_query_groups", head_num)  # different num_query_groups for 70B

+  head_size = model.cfg.get("kv_channels") or (hidden_size // head_num) # equivalent to hf's head_dim
-   head_size = hidden_size // head_num
    heads_per_group = head_num // num_query_groups
    qkv_total_dim = head_num + 2 * num_query_groups
```

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**PR Type**:
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- [x] Bugfix
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## Who can review?
@kevalmorabia97 

# Additional Information
Pruned values corresponding to huggingface's config.json should be updated.
I added `head_dim (hf)` to hf's config.json with the same value of `kv_channels (nemo)`
