Model Merging in Pre-training of Large Language Models

Model merging has emerged as a promising technique for enhancing large language models, though its application in large-scale pre-training remains relatively unexplored. In this paper, we present a comprehensive investigation of model merging techniques during the pre-training process. Through extensive experiments with both dense and Mixture-of-Experts (MoE) architectures ranging from millions to over 100 billion parameters, we demonstrate that merging checkpoints trained with constant learning rates not only achieves significant performance improvements but also enables accurate prediction of annealing behavior. These improvements lead to both more efficient model development and significantly lower training costs. Our detailed ablation studies on merging strategies and hyperparameters provide new insights into the underlying mechanisms while uncovering novel applications. Through comprehensive experimental analysis, we offer the open-source community practical pre-training guidelines for effective model merging.

ByteCheckpoint: A Unified Checkpointing System for LLM Development

The development of real-world Large Language Models (LLMs) necessitates checkpointing of training states in persistent storage to mitigate potential software and hardware failures, as well as to facilitate checkpoint transferring within the training pipeline and across various tasks. Due to the immense size of LLMs, saving and loading checkpoints often incur intolerable minute-level stalls, significantly diminishing training efficiency. Besides, when transferring checkpoints across tasks, checkpoint resharding, defined as loading checkpoints into parallel configurations differing from those used for saving, is often required according to the characteristics and resource quota of specific tasks. Previous checkpointing systems [16,3,33,6] assume consistent parallel configurations, failing to address the complexities of checkpoint transformation during resharding. Furthermore, in the industry platform, developers create checkpoints from different training frameworks[23,36,21,11], each with its own unique storage and I/O logic. This diversity complicates the implementation of unified checkpoint management and optimization. To address these challenges, we introduce ByteCheckpoint, a PyTorch-native multi-framework LLM checkpointing system that supports automatic online checkpoint resharding. ByteCheckpoint employs a data/metadata disaggregated storage architecture, decoupling checkpoint storage from the adopted parallelism strategies and training frameworks. We design an efficient asynchronous tensor merging technique to settle the irregular tensor sharding problem and propose several I/O performance optimizations to significantly enhance the efficiency of checkpoint saving and loading. Experimental results demonstrate ByteCheckpoint's substantial advantages in reducing checkpoint saving (by up to 529.22X) and loading (by up to 3.51X) costs, compared to baseline methods.