LongLoRA: Efficient Fine-tuning of Long-Context Large Language Models
Written for the Research library (claude-opus-5-5) from the paper text, in our own words: the license "arXiv — non-exclusive license to distribute" does not allow redistributing the text itself. Original — arxiv.org/pdf/2309.12307
Summary
Extending the context window of a pre-trained LLM is usually very costly, because self-attention cost grows quadratically with sequence length. Earlier approaches such as Position Interpolation and FOT relied on full fine-tuning on clusters of 32–128 A100 GPUs or TPUs. LongLoRA makes this extension cheap by combining two ideas. First, during fine-tuning only, it replaces full attention with shifted sparse attention (S2-Attn). Tokens are split into groups, attention runs inside each group, and in half of the heads the tokens are shifted by half a group so information can pass between neighbouring groups. At inference the model returns to ordinary dense attention. Second, it shows that plain LoRA fails at long contexts unless the embedding and normalization layers are also trained. Applied to Llama2 7B/13B/70B, LongLoRA nearly matches full-attention, fully fine-tuned perplexity at a much lower cost. The authors also release LongAlpaca, a long instruction-following dataset, for supervised fine-tuning. This matters because long-context adaptation becomes feasible on a single multi-GPU server.
Key points
- S2-Attn needs only about two lines of training code and leaves the architecture unchanged at inference, so it works with Flash-Attention2. For example, a group size of 2048 approximates training at 8192 tokens.
- On PG19 validation, Llama2 7B fully fine-tuned on RedPajama scored these perplexities at 8192/16384/32768 tokens:
- S2-Attn: 8.04 / 8.03 / 8.08
- Full attention: 8.02 / 8.05 / 8.04
- Unshifted short attention: 8.29 / 8.83 / 9.47
- The extra trainable layers add very few parameters. In Llama2 7B, embedding is under 2% of parameters and normalization is at most 0.004%.
- On one 8× A100 machine, LongLoRA extends Llama2 7B from 4k to 100k context and Llama2 70B to 32k.
- Compared with full fine-tuning, memory use is up to 1.8× lower. Compared with standard LoRA, training is up to 1.8× faster, measured with proof-pile perplexity evaluation. Code, models and LongAlpaca are available at github.com/dvlab-research/LongLoRA.
Cited by
- PyramidKV: Dynamic KV Cache Compression based on Pyramidal Information Funneling
- Expanding Performance Boundaries of Open-Source Multimodal Models with Model, Data, and Test-Time Scaling
- LongRoPE: Extending LLM Context Window Beyond 2 Million Tokens
- Gemini 1.5: Unlocking multimodal understanding across millions of tokens of context
- HippoRAG: Neurobiologically Inspired Long-Term Memory for Large Language Models
- Parameter-Efficient Fine-Tuning for Large Models: A Comprehensive Survey
- KVQuant: Towards 10 Million Context Length LLM Inference with KV Cache Quantization
- RULER: What's the Real Context Size of Your Long-Context Language Models?
- HEBATRON: A Hebrew-Specialized Open-Weight Mixture-of-Experts Language Model
- LooGLE: Can Long-Context Language Models Understand Long Contexts?
- Long-context LLMs Struggle with Long In-context Learning
- The Unlocking Spell on Base LLMs: Rethinking Alignment via In-Context Learning
- A Comprehensive Overview of Large Language Models
- How Is LLM Reasoning Distracted by Irrelevant Context? An Analysis Using a Controlled Benchmark
- LlamaFactory: Unified Efficient Fine-Tuning of 100+ Language Models
Cite
@misc{chen2023longlora,
title = {{LongLoRA: Efficient Fine-tuning of Long-Context Large Language Models}},
author = {Chen, Yukang and Qian, Shengju and Tang, Haotian and Lai, Xin and Liu, Zhijian and Han, Song and Jia, Jiaya},
year = {2023},
doi = {10.48550/arxiv.2309.12307},
eprint = {2309.12307},
archivePrefix = {arXiv},
url = {https://doi.org/10.48550/arxiv.2309.12307}
}References
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