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High-Throughput and Memory-Efficient Zeroth-Order Fine-tuning LLMs with Distributed Parallel Computing

Paper · 2026 · Liangyu Wang, Huanyi Xie and Di Wang

Summary

Zeroth-order (ZO) optimization fine-tunes LLMs using only forward passes, which saves memory. The earlier ZO2 framework fits models as large as OPT-175B on one GPU by keeping parameters in CPU memory and streaming transformer blocks to the device. However, it runs on a single device and is slow. The authors present DistZO2, a framework that spreads ZO fine-tuning across a CPU plus several GPUs.

DistZO2 has three parts:

  • Perturbation Parallelism (PertP): the positively and negatively perturbed forward passes run on separate GPUs. A shared random seed keeps the perturbations identical, and only scalar losses are exchanged.
  • ZO-adapted DDP: devices synchronize the scalar projected gradient rather than full gradient tensors.
  • 2D layout: the two schemes are combined.

To relieve the PCIe bottleneck, parameter blocks are sliced and redistributed between GPUs over NVLink. On models up to OPT-175B, DistZO2 trains about three times faster than ZO2 while keeping GPU memory low. This makes full-parameter fine-tuning of very large models feasible on modest multi-GPU hardware.

Key points

  • On OPT-175B, DistZO2 reaches roughly a 3× speedup over ZO2, with GPU memory staying below about 20 GB.
  • PertP and the ZO-adapted DDP recover the throughput lost to ZO2's CPU offloading, bringing it to the level of MeZO.
  • Experiments covered OPT-1.3B through OPT-30B and OPT-175B.
  • In the 4-GPU 2D setup, placing PertP inner and DDP outer consistently gave higher throughput than the reverse order.
  • NVLink-based block slicing raised upload and offload bandwidth by up to 4.6×.
  • Scalability was verified on multi-node clusters of up to 16 GPUs. Pre-training, hybrid ZO/first-order methods and multimodal models are left for future work.

Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.

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Cite

Cite as Liangyu Wang, Huanyi Xie and Di Wang. 2026. High-Throughput and Memory-Efficient Zeroth-Order Fine-tuning LLMs with Distributed Parallel Computing. Findings of the Association for Computational Linguistics: ACL 2026.

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.18653/v1/2026.findings-acl.2128

@inproceedings{wang2026high,
  title = {{High-Throughput and Memory-Efficient Zeroth-Order Fine-tuning LLMs with Distributed Parallel Computing}},
  author = {Liangyu Wang, Huanyi Xie and Di Wang},
  booktitle = {Findings of the Association for Computational Linguistics: ACL 2026},
  year = {2026},
  doi = {10.18653/v1/2026.findings-acl.2128},
  url = {https://doi.org/10.18653/v1/2026.findings-acl.2128}
}

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