Adaptive Buffering Scheme for PCM/DRAM-Based Hybrid Memory Architecture

Abstract

Phase Change Memory (PCM) motivates new hybrid memory architecture that consists of PCM and DRAM. A critical issue in the PCM/DRAM-based hybrid memory architecture is how to devise efficient buffering schemes for heterogeneous memory. A feasible way is to use PCM as a page buffer in the memory hierarchy. Based on this assumption, this paper presents a new buffering scheme named FWQ-LRU for PCM/DRAM-based hybrid memory. FWQ-LRU proposes two new designs. First, it uses two queues for DRAM to identify write-cold DRAM pages, which will be moved to PCM during page replacement and page migrations. Second, to reduce PCM writes, it adopts an adaptive page migration mechanism to swap write-hot PCM pages with write-cold DRAM pages. Specially, FWQ-LRU devises a queue called FWQ (FIFO Write Queue) to detect write-hot PCM pages. Further, we periodically measure the page-migration benefits under the current workload to adjust the page migration policy for future requests. With this mechanism, write requests are mainly redirected to DRAM, and the writes to PCM are reduced. In addition, FWQ-LRU can maintain the same hit ratio as LRU. We conduct comparative trace-driven experiments and the results suggest the efficiency of our proposal.