Access characteristic guided read and write cost regulation for performance improvement on flash memory

The relatively high cost of write operations has become the performance bottleneck of flash memory. Write cost refers to the time needed to program a flash page using incremental-step pulse programming (ISPP), while read cost refers to the time needed to sense and transfer a page from the storage. If a flash page is written with a higher cost by using a finer step size during the ISPP process, it can be read with a relatively low cost due to the time saved in sensing and transferring, and vice versa. We introduce AGCR, an access characteristic guided cost regulation scheme that exploits this tradeoff to improve flash performance. Based on workload characteristics, logical pages receiving more reads will be written using a finer step size so that their read cost is reduced. Similarly, logical pages receiving more writes will be written using a coarser step size so that their write cost is reduced. Our evaluation shows that AGCR incurs negligible overhead, while improving performance by 15% on average, compared to previous approaches.