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[Bug fix] Avoid OOM when casting fp32 on NPU for GRPO with vLLM colocate #9335

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Merged
hjh0119 merged 7 commits into from
May 19, 2026
Merged

[Bug fix] Avoid OOM when casting fp32 on NPU for GRPO with vLLM colocate #9335

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dc5332b
avoid OOM when casting fp32 on NPU for GRPO with vLLM colocate
ys2025-AI May 13, 2026
9bfc878
Merge pull request #1 from ys2025-AI/fsdp2_npu
ys2025-AI May 13, 2026
b466051
Merge branch 'modelscope:main' into main
ys2025-AI May 13, 2026
b48494a
Update fsdp.py
ys2025-AI May 15, 2026
1f6ec9c
Merge branch 'modelscope:main' into main
ys2025-AI May 19, 2026
3e32487
Update fsdp.py
ys2025-AI May 19, 2026
0c4cbe2
Update fsdp.py
ys2025-AI May 19, 2026
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10 changes: 10 additions & 0 deletions swift/model/npu_patch/fsdp.py
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Original file line number Diff line number Diff line change
Expand Up @@ -26,7 +26,17 @@ def _cast_module_to_fp32_for_npu_if_needed(module: torch.nn.Module, accelerator:
# entering that path with bf16/fp16 parameters can fail before mixed
# precision policy has a chance to manage runtime compute dtype. Cast early
# while parameters are still on CPU or meta, so only dtype changes here.

# GRPO with vLLM colocate mode may preload the model onto NPU before
# Accelerator.prepare() is called. In that case, casting fp32 on NPU
# would temporarily duplicate the full model (bf16 + fp32), causing OOM.
# We move the model back to CPU first to free NPU memory, then cast.
try:
if param.device.type == 'npu':
import torch_npu
module = module.cpu()
torch_npu.npu.synchronize()
torch_npu.npu.empty_cache()
return module.to(torch.float32)
except Exception as exc:
raise NPUCastError(f'Failed to cast {module.__class__.__name__} to fp32.') from exc
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