RTCache: an Efficient Remapping Table Cache for NVM Wear-Leveling

NVM provides a more generalized high-density memory media with DRAM-like performance and non-volatile nature to provide persistent data accesses to computing devices. Due to the poor write tolerance of NVM, wear-leveling strategies are essential in NVM. We find that the remapping table accesses become a neglected performance bottleneck when deploying wear-leveling strategies in NVM controllers, and contiguity-based CPU address mapping caching optimization strategies cannot be adapted due to the randomized mappings introduced by wear-leveling strategies. In this paper, we present RTCache, an efficient caching mechanism designed to accelerate access performance of the wear-leveling remapping table in NVM controllers. We propose a two-level mapping cache to enhance the cache utilization, consequently improving the cache hit ratio. Notably, RTCache incorporates a victim cache to improve the efficiency of RTCache for discretely accessed pages. Furthermore, RTCache adopts a cache-friendly remapping table memory structure, mitigating the challenges posed by access amplification due to RTCache misses. Experimental results show that RTCache can significantly improve the performance of NVM with wear-leveling strategies, and the negative impact on the system performance is reduced to an acceptable level.