How Much Knowledge Can You Pack into a LoRA Adapter without Harming LLM?
Authors: name: Sergey Pletenev; name: Maria Marina; name: Daniil Moskovskiy; name: Vasily Konovalov; name: Pavel Braslavski; name: Alexander Panchenko; name: Mikhail Salnikov
Published: 2025-02-20 12:31:03

Abstract: The performance of Large Language Models (LLMs) on many tasks is greatly
limited by the knowledge learned during pre-training and stored in the model's
parameters. Low-rank adaptation (LoRA) is a popular and efficient training
technique for updating or domain-specific adaptation of LLMs. In this study, we
investigate how new facts can be incorporated into the LLM using LoRA without
compromising the previously learned knowledge. We fine-tuned
Llama-3.1-8B-instruct using LoRA with varying amounts of new knowledge. Our
experiments have shown that the best results are obtained when the training
data contains a mixture of known and new facts. However, this approach is still
potentially harmful because the model's performance on external
question-answering benchmarks declines after such fine-tuning. When the
training data is biased towards certain entities, the model tends to regress to
few overrepresented answers. In addition, we found that the model becomes more
confident and refuses to provide an answer in only few cases. These findings
highlight the potential pitfalls of LoRA-based LLM updates and underscore the
importance of training data composition and tuning parameters to balance new
knowledge integration and general model capabilities.