Fast Model Editing at Scale
Eric Mitchell and Charles Lin and Antoine Bosselut and Chelsea Finn and Christopher D. Manning
arXiv e-Print archive - 2021 via Local arXiv
Keywords: cs.LG, cs.AI, cs.CL
First published: 2024/04/28 (just now)
Abstract: While large pre-trained models have enabled impressive results on a variety of downstream tasks, the largest existing models still make errors, and even accurate predictions may become outdated over time. Because detecting all such failures at training time is impossible, enabling both developers and end users of such models to correct inaccurate outputs while leaving the model otherwise intact is desirable. However, the distributed, black-box nature of the representations learned by large neural networks makes producing such targeted edits difficult. If presented with only a single problematic input and new desired output, fine-tuning approaches tend to overfit; other editing algorithms are either computationally infeasible or simply ineffective when applied to very large models. To enable easy post-hoc editing at scale, we propose Model Editor Networks using Gradient Decomposition (MEND), a collection of small auxiliary editing networks that use a single desired input-output pair to make fast, local edits to a pre-trained model's behavior. MEND learns to transform the gradient obtained by standard fine-tuning, using a low-rank decomposition of the gradient to make the parameterization of this transformation tractable. MEND can be trained on a single GPU in less than a day even for 10 billion+ parameter models; once trained MEND enables rapid application of new edits to the pre-trained model. Our experiments with T5, GPT, BERT, and BART models show that MEND is the only approach to model editing that effectively edits the behavior of models with more than 10 billion parameters. Code and data available at https://sites.google.com/view/mend-editing.
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Eric Mitchell and Charles Lin and Antoine Bosselut and Chelsea Finn and Christopher D. Manning
arXiv e-Print archive - 2021 via Local arXiv
Keywords: cs.LG, cs.AI, cs.CL
First published: 2024/04/28 (just now)
Abstract: While large pre-trained models have enabled impressive results on a variety of downstream tasks, the largest existing models still make errors, and even accurate predictions may become outdated over time. Because detecting all such failures at training time is impossible, enabling both developers and end users of such models to correct inaccurate outputs while leaving the model otherwise intact is desirable. However, the distributed, black-box nature of the representations learned by large neural networks makes producing such targeted edits difficult. If presented with only a single problematic input and new desired output, fine-tuning approaches tend to overfit; other editing algorithms are either computationally infeasible or simply ineffective when applied to very large models. To enable easy post-hoc editing at scale, we propose Model Editor Networks using Gradient Decomposition (MEND), a collection of small auxiliary editing networks that use a single desired input-output pair to make fast, local edits to a pre-trained model's behavior. MEND learns to transform the gradient obtained by standard fine-tuning, using a low-rank decomposition of the gradient to make the parameterization of this transformation tractable. MEND can be trained on a single GPU in less than a day even for 10 billion+ parameter models; once trained MEND enables rapid application of new edits to the pre-trained model. Our experiments with T5, GPT, BERT, and BART models show that MEND is the only approach to model editing that effectively edits the behavior of models with more than 10 billion parameters. Code and data available at https://sites.google.com/view/mend-editing.
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The goal of this work is to edit the model’s weights given new edit pairs ($x_e, y_e$) at test time. They achieve this by learning a "model editor network" that takes a fine tuning gradient computed from ($x_e, y_e$) and transforms this into a weight update.
$$ f(\nabla W_l) \rightarrow \tilde\nabla W_l$$
The editor network is parameterized by the layer that it is predicting using a FiLM style scale and shift.
The editor network is trained on a small set of examples ($D^{tr}_{edit}$). The paper states that this dataset contains edits that are similar to the "the types of edits that will be made." which is interesting because it introduces generalization limitations to the potential edits.
An extra loss term is used to prevent unintended changes for other inputs to the model (called $x_{loc}$). This is achieved with the following loss that will maintain the predictions to be the same value.
$$L_{loc} = KL(p_{\theta_W}(\cdot | x_{loc}) \| p_{\theta_\tilde{W}}(\cdot | x_{loc}))$$
Some intuition for why this works is editor network $f$ approximates full dataset gradient from just a single example so it is more efficient. It can reduce the change of elements of the weight matrix which were disruptive to the loss when it was trained, information that requires many training examples to uncover.
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