What is a good buffer cache replacement scheme for mobile flash storage?

Abstract

Smartphones are becoming ubiquitous and powerful. The Achilles' heel in such devices that limits performance is the storage. Low-end flash memory is the storage technology of choice in such devices due to energy, size, and cost considerations. In this paper, we take a critical look at the performance of flash on smartphones for mobile applications. Specifically, we ask the question whether the state-of-the-art buffer cache replacement schemes proposed thus far (both flash-agnostic and flash-aware ones) are the right ones for mobile flash storage. To answer this question, we first expose the limitations of current buffer cache performance evaluation methods, and propose a novel evaluation framework that is a hybrid between trace-driven simulation and real implementation of such schemes inside an operating system. Such an evaluation reveals some unexpected and surprising insights on the performance of buffer management schemes that contradicts conventional wisdom. Armed with this knowledge, we propose a new buffer cache replacement scheme called SpatialClock. Using our evaluation framework, we show the superior performance of SpatialClock relative to the state-of-the-art for mobile flash storage.