Architecting DDR5 DRAM caches for non-volatile memory systems

With the release of Intel's Optane DIMM, Non-Volatile Memories (NVMs) are emerging as viable alternatives to DRAM memories because of the advantage of higher capacity. However, the higher latency and lower bandwidth of Optane prevent it from outright replacing DRAM. A prevailing strategy is to employ existing DRAM as a data cache for Optane, thereby achieving overall benefit in capacity, bandwidth, and latency. In this paper, we inspect new features in DDR5 to better support the DRAM cache design for Optane. Specifically, we leverage the two-level ECC scheme, i.e., DIMM ECC and on-die ECC, in DDR5 to construct a narrower channel for tag probing and propose a new operation for fast cache replacement. Experimental results show that our proposed strategy can achieve, on average, 26% performance improvement.