Sparse Structure Search for Parameter-Efficient Tuning
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Adapting large pre-trained models (PTMs) through fine-tuning imposes prohibitive computational and storage burdens. Recent studies of parameter-efficient tuning (PET) find that only optimizing a small portion of parameters conditioned on PTMs could yield on-par performance compared to conventional fine-tuning. Generally, PET methods exquisitely design parameter-efficient modules (PET modules) which could be applied to arbitrary fine-grained positions inside PTMs. However, the effectiveness of these fine-grained positions largely relies on sophisticated manual designation, thereby usually producing sub-optimal results. In contrast to the manual designation, we explore constructing PET modules in an automatic manner. We automatically Search for the Sparse Structure of Parameter-Efficient Tuning (S^3PET). Based on a unified framework of various PET methods, S^3PET conducts the differentiable PET structure search through bi-level optimization and proposes shifted global sigmoid method to explicitly control the number of trainable parameters. Extensive experiments show that S^3PET surpasses manual and random structures with less trainable parameters. The searched structures preserve more than 99% fine-tuning performance with 0.01% trainable parameters. Moreover, the advantage of S^3PET is amplified with extremely low trainable parameters budgets (0.0009%∼0.01%). The searched structures are transferable and explainable, providing suggestions and guidance for the future design of PET methods.
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