instruct-goose 0.0.3

Implementation of Reinforcement Learning from Human Feedback (RLHF)

InstructGoose - 🚧 WORK IN PROGRESS 🚧

Paper: InstructGPT - Training language models to follow instructions with human feedback

Install

Install from PipPy

pip install instruct-goose

Install directly from the source code

git clone https://github.com/xrsrke/instructGOOSE.git
cd instructGOOSE
pip install -e .

Train the RL-based language model

from transformers import AutoTokenizer, AutoModelForCausalLM
from datasets import load_dataset

import torch
from torch.utils.data import DataLoader
from torch import optim

from instruct_goose import Agent, RewardModel, RLHFTrainer, RLHFConfig, create_reference_model

Step 1: Load dataset

dataset = load_dataset("imdb", split="train")
train_dataloader = DataLoader(dataset, batch_size=4, shuffle=True)

Step 2: Load the pre-trained model and tokenizer

model_base = AutoModelForCausalLM.from_pretrained("gpt2")
reward_model = RewardModel("gpt2")

tokenizer = AutoTokenizer.from_pretrained("gpt2")
eos_token_id = tokenizer.eos_token_id
tokenizer.pad_token = tokenizer.eos_token

Step 3: Create the RL-based language model agent and the reference model

model = Agent(model_base)
ref_model = create_reference_model(model)

Step 4: Train it

max_new_tokens = 20
generation_kwargs = {
    "min_length":-1,
    "top_k": 0.0,
    "top_p": 1.0,
    "do_sample": True,
    "pad_token_id": tokenizer.eos_token_id,
    "max_new_tokens": max_new_tokens
}

config = RLHFConfig()
N_EPOCH = 100
trainer = RLHFTrainer(model, ref_model, config)
optimizer = optim.SGD(model.parameters(), lr=1e-3)

for epoch in range(N_EPOCH):
    for batch in train_dataloader:
        inputs = tokenizer(batch["text"], padding=True, truncation=True, return_tensors="pt")
        responses = model.generate(
            inputs["input_ids"], attention_mask=inputs["attention_mask"],
            **generation_kwargs
        )
        
        # extract the generated text
        responses = responses[:, -max_new_tokens:]
        
        # evaluate from the reward model
        with torch.no_grad():
            text_input_ids = torch.stack([torch.concat([q, r]) for q, r in zip(inputs["input_ids"], responses)], dim=0)
            texts = tokenizer.batch_decode(text_input_ids, skip_special_tokens=True)
            rewards = reward_model(texts)
        
        # calculate PPO loss
        loss = trainer.compute_loss(inputs["input_ids"], responses, rewards)
        optimizer.zero_grad()
        loss.backward()
        optimizer.step()
        print(f"loss={loss}")

TODO

• Add support custom reward function
• Add support custom value function
• Add support non-transformer models

Questions

• In the context of RLHF, how to calculate the $L_t^{V F}(\theta)$,
  • Like it’s a function of the PPO agent uses to predict how much reward it gets if generates the sequence?
• Does the RL model and the SFT model use the same tokenizer? Yes
• I don’t know how to returns the logit of the generation model
• Does the PPO Agent (Language Model) has a value network just like the regular PPO Agent?
• I don’t understand how to calculate the advantage in PPO

Resources

I used these resources to implement this

• Copied the load_yaml function from https://github.com/Dahoas/reward-modeling
• How to build a dataset to train reward model: https://wandb.ai/carperai/summarize_RLHF/reports/Implementing-RLHF-Learning-to-Summarize-with-trlX–VmlldzozMzAwODM2
• How to add value head in PPO agent: https://github.com/lvwerra/trl
• How to calculate the loss of PPO agent: https://github.com/lvwerra/trl/blob/main/trl/trainer/ppo_trainer.py
• How to use PPO to train RLHF agent: https://github.com/voidful/TextRL
• How PPO works: https://github.com/vwxyzjn/cleanrl/blob/master/cleanrl/ppo.py
• Copied the compute advantages and returns from TLR: https://github.com/lvwerra/trl/blob/d2e8bcf8373726fb92d2110c500f7df6d0bd566d/trl/trainer/ppo_trainer.py#L686