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fix: use meta device in disable_fp8 to avoid VRAM spike (#616)

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When swapping Float8Linear to Linear in disable_fp8 context manager,
using device=fp8_module.weight.device directly allocates new tensors
on GPU, causing unnecessary VRAM spike (~1GB for large models).

This fix uses device='meta' to avoid physical memory allocation,
then swaps in the weight tensor reference. This eliminates the
unnecessary VRAM spike during evaluation phase.

Fixes issue #592

Co-authored-by: RoomWithOutRoof <roomwithoutroof@sparklab.ai>
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RoomWithOutRoof 2026-03-26 05:24:57 +08:00 committed by GitHub
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scripts/base_train.py
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@ -218,12 +218,13 @@ def disable_fp8(model):
return
# Swap Float8Linear -> Linear (our custom class that casts weights to match input dtype)
# Use device="meta" to avoid VRAM spike - the weight tensor will be swapped in afterwards
for parent, attr_name, fp8_module in fp8_locations:
linear = Linear(
fp8_module.in_features,
fp8_module.out_features,
bias=fp8_module.bias is not None,
device=fp8_module.weight.device,
device="meta", # Use meta device to avoid unnecessary VRAM allocation
dtype=fp8_module.weight.dtype,
)
linear.weight = fp8_module.weight # share, don't copy