MPO: An Efficient Post-Processing Framework for Mixing Diverse Preference Alignment
This addresses the challenge of efficiently handling competing and heterogeneous human preferences in RLHF for LLMs, offering a more stable and cost-effective alternative to existing methods.
The paper tackles the problem of aligning large language models with diverse human preferences by proposing MPO, a post-processing framework that log-linearly combines single-objective policies, achieving balanced performance across preferences with significantly reduced computational costs.
Reinforcement Learning from Human Feedback (RLHF) has shown promise in aligning large language models (LLMs). Yet its reliance on a singular reward model often overlooks the diversity of human preferences. Recent approaches address this limitation by leveraging multi-dimensional feedback to fine-tune corresponding reward models and train LLMs using reinforcement learning. However, the process is costly and unstable, especially given the competing and heterogeneous nature of human preferences. In this paper, we propose Mixing Preference Optimization (MPO), a post-processing framework for aggregating single-objective policies as an alternative to both multi-objective RLHF (MORLHF) and MaxMin-RLHF. MPO avoids alignment from scratch. Instead, it log-linearly combines existing policies into a unified one with the weight of each policy computed via a batch stochastic mirror descent. Empirical results demonstrate that MPO achieves balanced performance across diverse preferences, outperforming or matching existing models with significantly reduced computational costs.