NVPC: A Transparent NVM Page Cache

Towards a compatible utilization of NVM, NVM-specialized kernel file systems and NVM-based disk file system accelerators have been proposed. However, these studies only focus on one or several characteristics of NVM, while failing to exploit its best practice by putting NVM in the proper position of the whole storage stack. In this paper, we present NVPC, a transparent acceleration to existing kernel file systems with an NVM-enhanced page cache. The acceleration lies in two aspects, respectively matching the desperate needs of existing disk file systems: sync writes and cache-missed operations. Besides, the fast DRAM page cache is preserved for cache-hit operations. For sync writes, a high-performance log-based sync absorbing area is provided to redirect data destination from the slow disk to the fast NVM. Meanwhile, the byte-addressable feature of NVM is used to prevent write amplification. For cache-missed operations, NVPC makes use of the idle space on NVM to extend the DRAM page cache, so that more and larger workloads can fit into the cache. NVPC is entirely implemented as a page cache, thus can provide efficient speed-up to disk file systems with full transparency to users and full compatibility to lower file systems. In Filebench macro-benchmarks, NVPC achieves at most 3.55x, 2.84x, and 2.64x faster than NOVA, Ext-4, and SPFS. In RocksDB workloads with working set larger than DRAM, NVPC achieves 1.12x, 2.59x, and 2.11x faster than NOVA, Ext-4, and SPFS. Meanwhile, NVPC gains positive revenue from NOVA, Ext-4, and SPFS in 62.5% of the tested cases in our read/write/sync mixed evaluation, demonstrating that NVPC is more balanced and adaptive to complex real-world workloads. Experimental results also show that NVPC is the only method that accelerates Ext-4 in particular cases for up to 15.19x, with no slow-down to any other use cases.