Sub-Linear Memory: How to Make Performers SLiM

Valerii Likhosherstov · Krzysztof Choromanski · Jared Quincy Davis · Xingyou Song · Adrian Weller

Keywords: [ Transformers ]

[ Abstract ]
[ OpenReview
Wed 8 Dec 4:30 p.m. PST — 6 p.m. PST

Abstract: Transformer architectures have become very popular yet the original implementation requires $O(L^2)$ in serial time and memory as functions of input length $L$. Recent works proposed various linear self-attention mechanisms, scaling only as $O(L)$ for serial computation. We conduct a thorough complexity analysis of Performers, a class which includes most recent linear Transformer mechanisms. We note a remarkable computational flexibility: the gradient computation can be performed with no approximations using sublinear memory as a function of $L$ (in addition to negligible storage for the input sequence), at a cost of greater time complexity in the parallel setting. In the extreme case, a Performer consumes only $O(1)$ memory, and still requires $O(L)$ time. Due to complete backward-compatibility, this discovered time-memory tradeoff can be used for fine-tuning on low-memory devices in a decentralized fashion without any server computations.

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