Reducing Journaling Overhead with Hybrid Buffer Cache

Abstract

Journaling technique is widely used in modern file systems for high reliability and fast recovery from system failures. However, journaling mechanism accounts for extra journal traffic flushed from the buffer cache to storage, greatly impeding the performance of file systems. Emerging non-volatile memory (NVM) technologies bring a new perspective of resolving this issue. But replacing DRAM with NVM as the whole buffer cache encounters the challenge of limited lifetime of NVM. As such, in this paper, we exploit a hybrid NVM-DRAM buffer cache architecture to optimize the journaling overhead using the non-volatility of NVM and the unlimited write endurance of DRAM. We propose a novel page management policy to direct page placement and migration while ensuring DRAM absorb most writes. Besides, a write-burst predictor is presented to further reduce write activities on NVM to prolong the lifespan of the hybrid buffer cache. Furthermore, we present a hybrid-commit journaling scheme to support the in-place commit of NVM and the in-memory commit of DRAM. We implement the proposed techniques on Linux 2.6.38 and measure the performance with various file I/O benchmarks. The experimental results show that our scheme significantly improves the I/O performance compared with the existing Linux buffer cache with ext4 and prolongs the lifetime compared with the NVM based buffer cache.