Q-GaLore: Quantized GaLore with INT4 Projection and Layer-Adaptive
  Low-Rank Gradients
Authors: name: Zhenyu Zhang; name: Ajay Jaiswal; name: Lu Yin; name: Shiwei Liu; name: Jiawei Zhao; name: Yuandong Tian; name: Zhangyang Wang
Published: 2024-07-11 08:42:58

Abstract: Training Large Language Models (LLMs) is memory-intensive due to the large
number of parameters and associated optimization states. GaLore, a recent
method, reduces memory usage by projecting weight gradients into a low-rank
subspace without compromising performance. However, GaLore relies on
time-consuming Singular Value Decomposition (SVD) operations to identify the
subspace, and the frequent subspace updates lead to significant training time
overhead. Moreover, GaLore offers minimal improvements in accuracy and
efficiency compared to LoRA in more accessible fine-tuning scenarios. To
address these limitations, we introduce Q-Galore, a novel approach that
substantially reduces memory usage by combining quantization and low-rank
projection, surpassing the benefits of GaLore. Our method is based on two key
observations: (i) the gradient subspace exhibits diverse properties, with some
layers converging early in training while others are subject to frequent
changes; (ii) the projection matrices are highly resilient to low-bit
quantization. Leveraging these insights, Q-GaLore adaptively updates the
gradient subspace based on its convergence statistics, achieving comparable
performance while significantly reducing the number of SVD operations. We
maintain the projection matrices in INT4 format and weights in INT8 format,
incorporating stochastic rounding to capture accumulated gradient information.
This approach enables a high-precision training trajectory using only
low-precision weights. We demonstrate that Q-GaLore achieves highly competitive
performance with exceptional memory efficiency. At pre-training, Q-GaLore
facilitates training a LLaMA-7B model from scratch on a single NVIDIA RTX 4060
Ti with only 16 GB memory. At fine-tuning, it reduces memory consumption by up
to 50% compared to LoRA and GaLore, while consistently outperforming QLoRA at
the same memory cost.