[Meirtz]

What

PP>1 export falls back to bridge.generate_pipeline_layout(...) when run_config.yaml cannot provide a usable layout — exactly like the import path already does.

Why (round-trip bug)

import → export of a DeepSeek-V4 checkpoint at PP>1 currently fails with AssertionError: pipeline_model_parallel_layout must be set when using hash MoE layers with pipeline parallelism (PP > 1).

Root cause: by save time the provider's layout has been finalized into a PipelineParallelLayerLayout object, and run_config.yaml serializes it as an instantiation stub — the actual layout data is lost:

pipeline_model_parallel_layout:
  _call_: true
  _target_: megatron.core.transformer.pipeline_parallel_layer_layout.PipelineParallelLayerLayout

The export-side reader only accepts a list, finds the stub, and the provider then asserts. Reproduced on a full DeepSeek-V4-Flash TP1/PP4/EP8 checkpoint (imported with this same script); with the fallback the export proceeds.

A deeper fix would be serializing the layout in its list form in run_config.yaml (checkpointing owners' call); this script-level fallback restores the import→export round trip now.

Notes

• AI-assisted (Claude); analysis, repro and review by the human author.

🤖 Generated with Claude Code

[Meirtz]

/ok to test 3acf617

[Meirtz]

Validated end-to-end on 32x GB300 (TP1/PP4/EP8) with real DeepSeek-V4-Flash weights.

The original script-level fallback turned out to be insufficient on its own: load_megatron_model rebuilds the provider from the checkpoint's run_config.yaml, where the layout is the serialized object stub, so the PP>1 assert still fired inside build_and_load_model. The second commit forwards the resolved layout through mp_overrides (and declares the field in ModelParallelKwargs).

Test flow: fresh HF->Megatron import (run_config carries the stub — confirmed before export), then export with no manual repair. The fallback log line fires (Auto-generated pipeline layout for PP=4 (43 layers, 1 MTP)) and the export completes with 69187 tensors / 34167 scales, identical counts to a reference export from a hand-repaired run_config.