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Adapting Language Models to Compress Long Contexts (EMNLP'23)

This is the official implementation of the paper Adapting Language Models to Compress Long Contexts, in which we train AutoCompressors which are language models with the new capability to (1) compress context information into a small set of summary vectors and (2) reason over these summary vectors which are passed to the model as soft prompts.

Now supporting .generate() and releasing an AutoCompressor based on Llama-2-7b.

Example:

Example use of the API with a pre-trained AutoCompressor model:

import torch
from transformers import AutoTokenizer
from auto_compressor import LlamaAutoCompressorModel, AutoCompressorModel

# Load AutoCompressor trained by compressing 6k tokens in 4 compression steps
tokenizer = AutoTokenizer.from_pretrained("princeton-nlp/AutoCompressor-Llama-2-7b-6k")
# Need bfloat16 + cuda to run Llama model with flash attention
model = LlamaAutoCompressorModel.from_pretrained("princeton-nlp/AutoCompressor-Llama-2-7b-6k", torch_dtype=torch.bfloat16).eval().cuda()

prompt = 'The first name of the current US president is "'
prompt_tokens = tokenizer(prompt, add_special_tokens=False, return_tensors="pt").input_ids.cuda()

context = """Joe Biden, born in Scranton, Pennsylvania, on November 20, 1942, had a modest upbringing in a middle-class family. He attended the University of Delaware, where he double-majored in history and political science, graduating in 1965. Afterward, he earned his law degree from Syracuse University College of Law in 1968.\nBiden's early political career began in 1970 when he was elected to the New Castle County Council in Delaware. In 1972, tragedy struck when his wife Neilia and 1-year-old daughter Naomi were killed in a car accident, and his two sons, Beau and Hunter, were injured. Despite this devastating loss, Biden chose to honor his commitment and was sworn in as a senator by his sons' hospital bedsides.\nHe went on to serve as the United States Senator from Delaware for six terms, from 1973 to 2009. During his time in the Senate, Biden was involved in various committees and was particularly known for his expertise in foreign affairs, serving as the chairman of the Senate Foreign Relations Committee on multiple occasions.\nIn 2008, Joe Biden was selected as the running mate for Barack Obama, who went on to win the presidential election. As Vice President, Biden played an integral role in the Obama administration, helping to shape policies and handling issues such as economic recovery, foreign relations, and the implementation of the Affordable Care Act (ACA), commonly known as Obamacare.\nAfter completing two terms as Vice President, Joe Biden decided to run for the presidency in 2020. He secured the Democratic nomination and faced the incumbent President Donald Trump in the general election. Biden campaigned on a platform of unity, promising to heal the divisions in the country and tackle pressing issues, including the COVID-19 pandemic, climate change, racial justice, and economic inequality.\nIn the November 2020 election, Biden emerged victorious, and on January 20, 2021, he was inaugurated as the 46th President of the United States. At the age of 78, Biden became the oldest person to assume the presidency in American history.\nAs President, Joe Biden has worked to implement his agenda, focusing on various initiatives, such as infrastructure investment, climate action, immigration reform, and expanding access to healthcare. He has emphasized the importance of diplomacy in international relations and has sought to rebuild alliances with global partners.\nThroughout his long career in public service, Joe Biden has been recognized for his commitment to bipartisanship, empathy, and his dedication to working-class issues. He continues to navigate the challenges facing the nation, striving to bring the country together and create positive change for all Americans."""
context_tokens = tokenizer(context, add_special_tokens=False, return_tensors="pt").input_ids.cuda()

summary_vectors = model(context_tokens, output_softprompt=True).softprompt
print(f"Compressing {context_tokens.size(1)} tokens to {summary_vectors.size(1)} summary vectors")
# >>> Compressing 660 tokens to 50 summary vectors

generation_with_summary_vecs = model.generate(prompt_tokens, do_sample=False, softprompt=summary_vectors, max_new_tokens=12)[0]
print("Generation w/ summary vectors:\n" + tokenizer.decode(generation_with_summary_vecs))
# >>> The first name of the current US president is "Joe" and the last name is "Biden".

next_tokens_without_context = model.generate(prompt_tokens, do_sample=False, max_new_tokens=11)[0]
print("Generation w/o context:\n" + tokenizer.decode(next_tokens_without_context))
# >>> The first name of the current US president is "Donald" and the last name is "Trump".

Install

Setup a new environment and install pytorch version 2.1.0, followed by these libraries

pip install packaging
pip install transformers==4.34.0 datasets==2.13.4 accelerate==0.24.1 sentencepiece==0.1.99 flash-attn==2.3.5 wandb
# Flash rotary embeddings (requires setting correct CUDA_HOME variable)
pip install git+https://github.com/Dao-AILab/flash-attention.git#subdirectory=csrc/rotary

Then clone this repo and navigate to the repository root to run scripts or import the libraries.

Training

train.sh is the main method for training AutoCompressors and defines the most important hyperparameters for train.py. You may have adjust some setting, like the number GPUs, depending on the system. The script should be easy to get started with, since it uses pre-tokenized datasets from the huggingface hub.

Notes on Flash Attention

We use Flash Attention which lowers the memory requirements during training substantially.

Llama architecture: We implement flash attention via the Flash Attention package. These kernels require training and running the model on cuda in mixed or half precision.

OPT architecture: We implement flash attention via torch.nn.functional.scaled_dot_product_attention, which you can use by adding --fast_attention to train.sh. Note that this is experimental and requires the preview version of pytorch. We have encountered some issues with using fast attention during evaluation, especially with use_cache=True, so we recommend only using the fast attention during training.

Pre-trained Models

All the fine-tuned models from our paper can be found on Huggingface hub:

Loading Models

To load Llama-20based AutoCompressor models, import LlamaAutoCompressModel:

from transformers import AutoTokenizer
from auto_compressor import LlamaAutoCompressorModel

tokenizer = AutoTokenizer.from_pretrained("princeton-nlp/AutoCompressor-Llama-2-7b-6k")
model = LlamaAutoCompressModel.from_pretrained("princeton-nlp/AutoCompressor-Llama-2-7b-6k")

To load OPT-based AutoCompressor models, import OPTAutoCompressorModel:

from transformers import AutoTokenizer
from auto_compressor import OPTAutoCompressorModel

tokenizer = AutoTokenizer.from_pretrained("princeton-nlp/AutoCompressor-2.7b-6k")
model = OPTAutoCompressorModel.from_pretrained("princeton-nlp/AutoCompressor-2.7b-6k")

Summary Vectors

The summary vectors for a given context can be obtained in two ways:

1. Explicitly: Call the model with out = model(input_ids, attention_mask, ..., output_softprompt=True) and obtain the summary vectors as summary_vectors = out.softprompt which can be passed to further calls by model(..., softprompt=sumary_vectors).
2. Implicitly: Call the model with out = model(input_ids, segment_lengths=segment_lengths), where segment_lengths is a list of integers that should add up to the overall sequence length input_ids.size(1). After each segment, the model will automatically generate the summary vectors and prepend them to the next segment. This can still be combined with output_softprompt=True to generate the final summary vectors for the entire input. This is convenient for multi-step compression of long inputs, which would otherwise exceed the model's maximum position.

Bug or Questions?

If you have any questions related to the code or the paper, feel free to email Alexis and Alexander (achevalier@ias.edu, awettig@cs.princeton.edu). If you encounter a problem or bug when using the code, you can open an issue. Please try to specify the problem with detail so we can help you quickly!

Citation

@inproceedings{chevalier2023adapting,
    title = "Adapting Language Models to Compress Contexts",
    author = "Chevalier, Alexis  and
      Wettig, Alexander  and
      Ajith, Anirudh  and
      Chen, Danqi",
    editor = "Bouamor, Houda  and
      Pino, Juan  and
      Bali, Kalika",
    booktitle = "Proceedings of the 2023 Conference on Empirical Methods in Natural Language Processing",
    month = dec,
    year = "2023",
    address = "Singapore",
    publisher = "Association for Computational Linguistics",
    url = "https://aclanthology.org/2023.emnlp-main.232",
    doi = "10.18653/v1/2023.emnlp-main.232",
    pages = "3829--3846"
}