m-fsdp: wire use_precision_aware_optimizer from ddp_config to ParamAn… by rapatel · Pull Request #4024 · NVIDIA/Megatron-LM

rapatel · 2026-03-25T05:28:27Z

…dGradBuffer

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shjwudp · 2026-03-25T05:30:45Z

/ok to test 74ddff5

cspades

Nit: Needs README / PyPI package documentation for the new argument, and possibly any arguments in training.py should be set during DDPConfig init.

Can handle in a subsequent PR if not done here, thanks!

jaredcasper · 2026-03-25T16:11:02Z

+    """If true, Megatron-FSDP's ParamAndGradBuffer uses the precision-aware optimizer
+      gradient path (e.g. `decoupled_grad` on optimizer parameters) instead of casting
+      main gradients to parameter dtype for `.grad`. Should match the training optimizer
+      setting (e.g. `--use-precision-aware-optimizer`).


command line args are only one way these dataclasses get populated, we shouldn't reference them in these docs. Is there an OptimizerConfig dataclass that has this option that should match?

I do see this - https://github.com/NVIDIA/Megatron-LM/blob/main/megatron/core/optimizer/optimizer_config.py#L187:

use_precision_aware_optimizer: bool = False """If true, allows optimizer-related tensors (master_param, gradients and optimizer states) to be set to lower precision. Defaults to False. """

Currently I think Megatron-Bridge and Megatron-FSDP only have this DDPConfig to shove all arguments into.

I think let's remove the reference to --use-precision-aware-optimizer to avoid confusing MLM vs. MBridge vs. etc. users of MCore, but I think having the same name as the attr in the OptimizerConfig might be helpful since they should be used together (when relevant, of course). Generally DDP-type classes need to know where to dump the grad.

I've gone ahead and updated the docstring.

gautham-kollu · 2026-03-30T16:33:55Z

/ok to test e9a02e3

…dGradBuffer

… MLM --use-precision-aware-optimizer. Signed-off-by: Cory Ye <cye@nvidia.com>

cspades · 2026-03-31T17:58:00Z

/ok to test 4d8cf30

cspades · 2026-03-31T20:12:06Z

/ok to test 038b141

jaredcasper

Approving, but can we make a plan for how to remove the megatron_fsdp_* args from ddpconfig?

cspades · 2026-04-01T17:26:34Z

Approving, but can we make a plan for how to remove the megatron_fsdp_* args from ddpconfig?

Yeah, I'll start a design doc with Megatron-Bridge and see if we can pass in DDPConfig and FSDPConfig separately, that's the main blocker at this point. Discussions can be had there.

svcnvidia-nemo-ci · 2026-04-01T20:25:19Z

🔄 Merge queue validation started!

You can track the progress here: https://github.com/NVIDIA/Megatron-LM/actions/runs/23869171336

NVIDIA#4024) Signed-off-by: Cory Ye <cye@nvidia.com> Co-authored-by: Cory Ye <cye@nvidia.com> Co-authored-by: Cory Ye <44509866+cspades@users.noreply.github.com>

NVIDIA#4024) Signed-off-by: Cory Ye <cye@nvidia.com> Co-authored-by: Cory Ye <cye@nvidia.com> Co-authored-by: Cory Ye <44509866+cspades@users.noreply.github.com> Signed-off-by: yhgalaxy <yhgalaxy@outlook.com>

NVIDIA#4024) Signed-off-by: Cory Ye <cye@nvidia.com> Co-authored-by: Cory Ye <cye@nvidia.com> Co-authored-by: Cory Ye <44509866+cspades@users.noreply.github.com> Signed-off-by: Jon Barker <jbarker@aws-cmh-slurm-1-vscode-02.cm.cluster>

# Description NVIDIA#4024 NVIDIA#3746 NVIDIA#2799 NVIDIA#3676 NVIDIA#4133 NVIDIA#3295 NVIDIA#3831 NVIDIA#3754 ## Type of change - [ ] New feature (non-breaking change which adds functionality) - [ ] Infra/Build change (changes to CI/CD workflows or build scripts) - [ ] Code refactoring - [ ] Documentation change - [x] Bug fix - [ ] Breaking change ## Changes - Content 1 - Content 2 - Content 3 - Content 4 ## Checklist - [ ] I have read and followed the contributing guidelines - [ ] The functionality is complete - [ ] I have commented my code, particularly in coverage report uploading steps - [ ] I have made corresponding changes to the documentation - [ ] My changes generate no new warnings - [ ] I have added/updated tests that prove my feature works - [ ] New and existing unit tests pass locally --------- Signed-off-by: Cory Ye <cye@nvidia.com> Signed-off-by: yexiaochuan <yexiaochuan@baidu.com> Signed-off-by: Akshat Kumar <akshat230405@gmail.com> Signed-off-by: Youngeun Kwon <youngeunk@nvidia.com> Signed-off-by: jinliangl <jinliangl@nvidia.com> Co-authored-by: Ritesh Patel <ripatel@nvidia.com> Co-authored-by: Cory Ye <cye@nvidia.com> Co-authored-by: Cory Ye <44509866+cspades@users.noreply.github.com> Co-authored-by: Xiaochuan Ye <tap91624@gmail.com> Co-authored-by: yexiaochuan <yexiaochuan@baidu.com> Co-authored-by: Akshat8510 <akshat230405@gmail.com> Co-authored-by: Kunlun Li <94586211+kunlunl@users.noreply.github.com> Co-authored-by: eternally-z <zzywzj@gmail.com> Co-authored-by: Philip Petrakian <ppetrakian@nvidia.com> Co-authored-by: Youngeun Kwon <youngeunk@nvidia.com> Co-authored-by: xuwchen <xuwenc@nvidia.com> Co-authored-by: Li Jinliang <jinliangl@nvidia.com>

NVIDIA#4024) Signed-off-by: Cory Ye <cye@nvidia.com> Co-authored-by: Cory Ye <cye@nvidia.com> Co-authored-by: Cory Ye <44509866+cspades@users.noreply.github.com>

rapatel requested review from a team as code owners March 25, 2026 05:28

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denys-fridman added a commit to denys-fridman/Megatron-LM that referenced this pull request Mar 25, 2026

Apply FSDP precision-aware optimizer patch from NVIDIA#4024

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Comment thread megatron/core/distributed/fsdp/src/megatron_fsdp/param_and_grad_buffer.py

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rapatel force-pushed the ripatel/fsdp_prec_optim_flag branch from 74ddff5 to e9a02e3 Compare March 25, 2026 18:49

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Comment thread megatron/core/distributed/distributed_data_parallel_config.py Outdated

m-fsdp: wire use_precision_aware_optimizer from ddp_config to ParamAn…

d11306c

…dGradBuffer

cspades force-pushed the ripatel/fsdp_prec_optim_flag branch from e9a02e3 to 7ef00ed Compare March 31, 2026 17:47

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cspades force-pushed the ripatel/fsdp_prec_optim_flag branch from 7ef00ed to 9e9aaab Compare March 31, 2026 17:50

Rename to megatron_fsdp_use_decoupled_grad and set automatically with…

cd0bf5e

… MLM --use-precision-aware-optimizer. Signed-off-by: Cory Ye <cye@nvidia.com>

cspades force-pushed the ripatel/fsdp_prec_optim_flag branch from 9e9aaab to cd0bf5e Compare March 31, 2026 17:56

Merge branch 'main' into ripatel/fsdp_prec_optim_flag

4d8cf30

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Merge branch 'main' into ripatel/fsdp_prec_optim_flag

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Merged via the queue into NVIDIA:main with commit fe5291f Apr 1, 2026
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cspades mentioned this pull request Apr 3, 2026

Fix incorrectly set decoupled_grad and DistOpt mechanics for MFSDP. #4133

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zhaoyinglia mentioned this pull request Jul 16, 2026

cherry-pick fix pr for megatron_fsdp flagos-ai/Megatron-LM-FL#79

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rapatel commented Mar 25, 2026

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