Segment and Conflict Aware Page Allocation and Migration in DRAM-PCM Hybrid Main Memory

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Phase change memory (PCM), given its nonvolatility, potential high density, and low standby power, is a promising candidate to be used as main memory in next generation computer systems. However, to hide its shortcomings of limited endurance and slow write performance, state-of-the-art solutions tend to construct a dynamic RAM (DRAM)-PCM hybrid memory and place write-intensive pages in DRAM. While existing optimizations to this hybrid architecture focus on tuning DRAM configurations to reduce the number of write operations to PCM, this paper explores the interactions between DRAM and PCM to improve both the performance and the endurance of a DRAM-PCM hybrid main memory. Specifically, it exploits the flexibility of mapping virtual pages to physical pages, and develops a proactive strategy to allocate pages taking both program segments and DRAM conflict misses into consideration, thus distributing those heavily written pages across different DRAM sets. Meanwhile, a lifetime-aware DRAM replacement algorithm and a conflict-aware page remapping strategy are proposed to further reduce DRAM misses and PCM writes. Experiments confirm that the proposed techniques are able to improve average memory hit time and reduce maximum PCM write counts thus enhancing both performance and lifetime of a DRAM-PCM hybrid main memory.