Buffer Cache Management for Combined MLC and SLC Flash Memories Using both Volatile and Nonvolatile RAMs

This paper presents a new buffer cache management scheme called DABC-NV for mixed MLC and SLC flash memories as the secondary storage and both byte-accessible NVRAM and conventional volatile RAM as their buffer caches. DABC-NV has four salient features. First, it allocates buffer cache space to MLC and SLC flash memories based on their I/O costs and then dynamically adjusts the allocated size according to the evolution of workloads. Second, it separately exploits read and write histories of block references, and thus it estimates future references of each operation more precisely. Third, it guarantees the complete consistency of write I/Os since all dirty data are cached in nonvolatile buffer caches. Fourth, metadata lists are maintained separately from cached blocks. This allows more efficient management of volatile and nonvolatile buffer caches based on read and write histories, respectively. Trace-driven simulations show that DABC-NV improves the I/O performance of embedded systems significantly. Specifically, it reduces I/O time by 24% on average compared to the CLOCK-NV algorithm.