Checkpoints

In this section, we present four key functionalities of NVIDIA NeMo related to checkpoint management:

1. Checkpoint Loading: Use the restore_from() method to load local .nemo checkpoint files.

2. Partial Checkpoint Conversion: Convert partially-trained .ckpt checkpoints to the .nemo format.

3. Community Checkpoint Conversion: Transition checkpoints from community sources, like HuggingFace, into the .nemo format.

4. Model Parallelism Adjustment: Modify model parallelism to efficiently train models that exceed the memory of a single GPU. NeMo employs both tensor (intra-layer) and pipeline (inter-layer) model parallelisms. Dive deeper with “Efficient Large-Scale Language Model Training on GPU Clusters Using Megatron-LM”. This tool aids in adjusting model parallelism, accommodating users who need to deploy on larger GPU arrays due to memory constraints.

A .nemo checkpoint is fundamentally a tar file that bundles the model configurations (given as a YAML file), model weights, and other pertinent artifacts like tokenizer models or vocabulary files. This consolidated design streamlines sharing, loading, tuning, evaluating, and inference.

Contrarily, the .ckpt file, created during PyTorch Lightning training, encompasses both the model weights and the optimizer states, usually employed to pick up training from a pause.

The subsequent sections elucidate instructions for the functionalities above, specifically tailored for deploying fully trained checkpoints for assessment or additional fine-tuning.

By default, NeMo saves checkpoints of trained models in the .nemo format. To save a model manually during training, use:

            

            
model.save_to(<checkpoint_path>.nemo)
        

To load a local .nemo checkpoint:

            

            
import nemo.collections.multimodal as nemo_multimodal
model = nemo_multimodal.models.<MODEL_BASE_CLASS>.restore_from(restore_path="<path/to/checkpoint/file.nemo>")
        

Replace <MODEL_BASE_CLASS> with the appropriate MM model class.

Only the last checkpoint is automatically saved in the .nemo format. If intermediate training checkpoints evaluation is required, a .nemo conversion might be necessary. For this, refer to the script at script:

            

            
python -m torch.distributed.launch --nproc_per_node=<tensor_model_parallel_size> * <pipeline_model_parallel_size> \
    examples/multimodal/convert_ckpt_to_nemo.py \
    --checkpoint_folder <path_to_PTL_checkpoints_folder> \
    --checkpoint_name <checkpoint_name> \
    --nemo_file_path <path_to_output_nemo_file> \
    --tensor_model_parallel_size <tensor_model_parallel_size> \
    --pipeline_model_parallel_size <pipeline_model_parallel_size>
        

CLIP Checkpoints

To migrate community checkpoints:

            

            
python examples/multimodal/foundation/clip/convert_external_clip_to_nemo.py \
    --arch=ViT-H-14 \
    --version=laion2b_s32b_b79k \
    --hparams_file=path/to/saved.yaml \
    --nemo_file_path=open_clip.nemo
        

Ensure the NeMo hparams file has the correct model architectural parameters, placed at path/to/saved.yaml. An example can be found in examples/multimodal/foundation/clip/conf/megatron_clip_config.yaml.

For OpenCLIP migrations, provide the architecture (arch) and version (version) according to the OpenCLIP model list. For Hugging Face conversions, set the version to huggingface and the architecture (arch) to the specific Hugging Face model identifier, e.g., yuvalkirstain/PickScore_v1.

CLIP Checkpoints

To adjust model parallelism from original model parallelism size to a new model parallelism size (Note: NeMo CLIP currently only supports pipeline_model_parallel_size=1):

            

            
python examples/nlp/language_modeling/megatron_change_num_partitions.py \
 --model_file=/path/to/source.nemo \
 --target_file=/path/to/target.nemo \
 --tensor_model_parallel_size=??? \
 --target_tensor_model_parallel_size=??? \
 --pipeline_model_parallel_size=-1 \
 --target_pipeline_model_parallel_size=1 \
 --precision=32 \
 --model_class="nemo.collections.multimodal.models.clip.megatron_clip_models.MegatronCLIPModel" \
 --tp_conversion_only