[megatron] fix async save

[Jintao-Huang]

No description provided.

[gemini-code-assist]

Summary of Changes

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This pull request addresses an issue with asynchronous checkpoint saving within the Megatron framework by centralizing and enhancing the checkpoint saving utility. It improves the flexibility and correctness of the save_mcore_checkpoint function, allowing callers to precisely manage output directories and asynchronous operations, particularly for merged checkpoints. This ensures a more robust and consistent checkpointing process.

Highlights

• Checkpoint Saving Refactor: Refactored the checkpoint merging logic in base.py to delegate the saving process to the save_mcore_checkpoint utility, ensuring consistent handling of merged checkpoints.
• Enhanced save_mcore_checkpoint Flexibility: Modified the save_mcore_checkpoint function to accept explicit output_dir and async_save parameters, providing greater control over checkpoint saving behavior.
• Loss Reporting Cleanup: Removed an unnecessary tuple conversion for reporting_loss in trainer.py, streamlining loss handling.

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Changelog

• swift/megatron/trainers/base.py
  • Replaced manual copying of latest_checkpointed_iteration.txt and common.pt with a call to save_mcore_checkpoint for merged checkpoints.
  • Ensured args.json is copied to the merged output directory.
• swift/megatron/trainers/trainer.py
  • Removed a redundant tuple conversion for the reporting_loss variable after an all-reduce operation.
• swift/megatron/utils/megatron_lm_utils.py
  • Added output_dir and async_save as optional parameters to the save_mcore_checkpoint function, allowing them to override values from args.
  • Updated the calculation of checkpoint_dir and the async_sharded_save parameter to use the new output_dir and async_save parameters.
  • Modified the finalization function (iter_finalize_fn) to use the provided output_dir for writing the latest_checkpointed_iteration.txt and for logging messages.

Activity

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Code Review

This pull request aims to fix an issue with asynchronous saving in Megatron. The changes primarily involve refactoring the save_mcore_checkpoint function to accept output_dir and async_save parameters, allowing for more flexible checkpointing logic. This is then used in BaseMegatronTrainer to handle merged LoRA checkpoints. However, I've found a critical bug in swift/megatron/trainers/base.py where a variable src_path is used without being defined, which will cause a NameError during execution. I've provided a suggestion to fix this.