  The data mixture for large language model pre-training significantly impacts
performance, yet how to determine an effective mixture remains unclear. We
propose RegMix to automatically identify a high-performing data mixture by
formulating it as a regression task. RegMix involves training a set of small
models with diverse data mixtures and fitting a regression model to predict
their performance given their respective mixtures. With the fitted regression
model, we simulate the top-ranked mixture and use it to train a large-scale
model with orders of magnitude more compute. To empirically validate RegMix, we
train 512 models with 1M parameters for 1B tokens of different mixtures to fit
the regression model and find the optimal mixture. Using this mixture we train
a 1B parameter model for 25B tokens (i.e. 1000x larger and 25x longer) which we
find performs best among 64 candidate 1B parameter models with other mixtures.
Further, our method demonstrates superior performance compared to human
selection and achieves results that match or surpass DoReMi, while utilizing
only 10% of the compute budget. Our experiments also show that (1) Data
mixtures significantly impact performance with single-task performance
variations of up to 14.6%; (2) Web corpora rather than data perceived as
high-quality like Wikipedia have the strongest positive correlation with
downstream performance; (3) Domains interact in complex ways often
contradicting common sense, thus automatic approaches like RegMix are needed;
(4) Data mixture effects transcend scaling laws, and our approach captures the
complexity by considering all domains together. Our code is available at
https://github.com/sail-sg/regmix.
