cp: fix: on GB200 use single-thread checkpoint save to avoid Cpu OOM (1703) into r0.5.0

[chtruong814]

beep boop [🤖]: Hi @guyueh1 👋,

we've cherry picked #1703 into  for you! 🚀

Please review and approve this cherry pick by your convenience!

Summary by CodeRabbit

• Chores
  • Updated internal dependency reference to latest version.

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[github-actions]

✅ Submodule Fast-Forward Check Results

Check based on commit: 98c9d6b (PR #1714 from cherry-pick-1703-r0.5.0)

✅ Submodules that are properly updated:

Megatron-LM: ✅ PR branch is ahead of r0.5.0 branch (fast-forward)

All submodule changes look good! ✨

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR updates the submodule reference for Megatron-LM from commit 25a62ed to b73ae5c. No functional or API changes are introduced; only the tracked submodule commit hash is modified.

Changes

Cohort / File(s)	Summary
Submodule reference 3rdparty/Megatron-LM-workspace/Megatron-LM	Updated submodule commit pointer from 25a62edf77b5130f888328ca8119d6a76117cf23 to b73ae5cdab9d409fcface2b2f3c375710abe6911

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Possibly related PRs

• chore: update megatron dev (11/21/2025) / mbridge (11/28/2025) #1568: Updates the same 3rdparty/Megatron-LM-workspace/Megatron-LM submodule reference pointer.

Suggested labels

GB200, r0.5.0

Suggested reviewers

• guyueh1
• terrykong

Pre-merge checks

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately reflects the cherry-pick operation into r0.5.0 and references the original fix for GB200 checkpoint save issues.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Test Results For Major Changes	✅ Passed	PR only updates submodule reference hash with no functional or public API changes, qualifying as minor changes.

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📥 Commits

Reviewing files that changed from the base of the PR and between 6e7a2f7 and 98c9d6b.

📒 Files selected for processing (1)

• 3rdparty/Megatron-LM-workspace/Megatron-LM

🧰 Additional context used

📓 Path-based instructions (1)

!(**/tests/**|**/test_*.py|**/test_*.sh)

📄 CodeRabbit inference engine (CODING_GUIDELINES.md)

Add the NVIDIA copyright header to all Python files and shell scripts (excluding tests). The header should include the current year

Files:

• 3rdparty/Megatron-LM-workspace/Megatron-LM

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🔇 Additional comments (1)

3rdparty/Megatron-LM-workspace/Megatron-LM (1)

1-1: Verify the submodule commit and cherry-pick completeness.

This PR cherry-picks commit #1703 (GB200 single-thread checkpoint save fix) into the r0.5.0 release branch. The only visible change is the submodule commit hash update. Please confirm:

1. The target commit hash (b73ae5c) in the Megatron-LM submodule contains the fix for checkpoint saving on GB200 as described in PR fix: on GB200 use single-thread checkpoint save to avoid Cpu OOM #1703.
2. No additional changes to the main repository are required to activate or support this fix.
3. The cherry-pick applies cleanly without conflicts.

You can verify the commit details by checking the Megatron-LM submodule's commit log.

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