bert2BERT: Towards Reusable Pretrained Language Models

TL;DR

bert2BERT introduces a method to transfer knowledge from smaller pre-trained models to larger ones, significantly reducing pre-training costs and improving efficiency across different transformer-based models.

Contribution

It extends function-preserving transfer techniques and proposes a two-stage pre-training method to enhance large model initialization and training efficiency.

Findings

Reduces pre-training computational costs by approximately 45-47%.

Demonstrates the method's applicability to various pre-trained models.

Achieves significant efficiency improvements over training from scratch.

Abstract

In recent years, researchers tend to pre-train ever-larger language models to explore the upper limit of deep models. However, large language model pre-training costs intensive computational resources and most of the models are trained from scratch without reusing the existing pre-trained models, which is wasteful. In this paper, we propose bert2BERT, which can effectively transfer the knowledge of an existing smaller pre-trained model (e.g., BERT_BASE) to a large model (e.g., BERT_LARGE) through parameter initialization and significantly improve the pre-training efficiency of the large model. Specifically, we extend the previous function-preserving on Transformer-based language model, and further improve it by proposing advanced knowledge for large model's initialization. In addition, a two-stage pre-training method is proposed to further accelerate the training process. We did extensive experiments on representative PLMs (e.g., BERT and GPT) and demonstrate that (1) our method can save a significant amount of training cost compared with baselines including learning from scratch, StackBERT and MSLT; (2) our method is generic and applicable to different types of pre-trained models. In particular, bert2BERT saves about 45% and 47% computational cost of pre-training BERT_BASE and GPT_BASE by reusing the models of almost their half sizes. The source code will be publicly available upon publication.