DWARM: A wear-aware memory management scheme for in-memory file systems

Emerging non-volatile memories (NVMs) are promised to revolutionize storage systems by providing fast, persistent data accesses on memory bus. A hybrid NVM/DRAM architecture that combines faster, volatile DRAM with slightly slower, denser NVM can harness the characteristics of both technologies. In order to fully take advantage of NVM, state-of-the-art in-memory file systems are designed to provide high performance and strong consistency guarantees. However, the free space management schemes of existing in-memory file systems can easily cause “hot spots” when updating data structures on NVM, leading to significant skewness in terms of writes to each data page. In this paper, we propose dynamic wear-aware range management (DWARM) scheme, a novel free space management technique for in-memory file systems. This scheme achieves wear-leveling with high performance for allocation/deallocation. The essential idea is to allocate less-written pages for each allocation request. Specifically, this scheme works by associating a write counter with each data page and updating the counters in the file write path. We build an “index” structure to fast locate the pages that have received less writes. The index divides the NVM pages into different subranges according to the write counters. Allocation always starts from the minimal subrange. Also, we propose Adaptive Wear Range Determination Algorithm to adjust the wear ranges dynamically. To accelerate lookup, we keep the index in DRAM and avoid the overhead of strong consistency by rebuilding the index in case of system failure. Experimental results show that this scheme can provide 4.9× to 158.1× wear-leveling improvement compared to the state-of-the-art memory management schemes. For application workloads, the DWARM strategy can improve the lifetime of NVM by up to 125×, 39×, and 25×, compared with the standard memory management schemes of PMFS, NOVA and SIMFS.