Dual composes inject PYTORCH_CUDA_ALLOC_CONF with expandable_segments:True for the PCIe path. detect_nvlink.sh used \, which kept that value on NVLink rigs and crashed custom all-reduce at CUDA graph profiling (vllm#42609). Assign max_split_size_mb:512 unconditionally when P2P is on.
Co-authored-by: Cursor <[email protected]>