LazyBarrier: Reconstructing Android IO Stack for Barrier-Enabled Flash Storage

Costly synchronous write---a.k.a., fsync()---is a common approach to preserve the storage order of data. Android smart-phones use No-Barrier by default to improve fsync() performance. Recently, Barrier-Enabled IO Stack (BEIOS) provides an efficient order-preserving method for flash storage by barrier write commands (BWCs). However, our evaluation shows that BEIOS suffers from performance degradation in multi-threaded scenarios since BWCs increase linearly with the number of threads. This paper proposes LazyBarrier, a new order-preserving IO stack mainly involving order-preserving write (OPW) Model, the Lazy Issue algorithm, modified F2FS, and Barrier Scheduling. OPW Model is based on Finite Automata and defines state transition in OPW. Lazy Issue is a novel algorithm that minimizes BWCs. F2FS is modified to support OPW, and Barrier Scheduling solves the ordering problem in multi-queue block layer. The experiments on Android smartphones show that, compared with BEIOS, LazyBarrier improves OPW performance by 73% and 29% under the FIO benchmark and in real applications respectively. And LazyBarrier also outperforms BEIOS by 19% in dbench workload in servers.