基于DRAM牺牲Cache的异构内存页迁移机制

DRAM-Based Victim Cache for Page Migration Mechanism on Heterogeneous Main Memory

当海量数据请求访问异构内存系统时,异构内存页在动态随机存储器(dynamic random access memory, DRAM)和非易失性存储器(non-volatile memory, NVM)之间进行频繁的往返迁移.然而,应用于传统内存页的迁移策略难以适应内存页"冷""热"度的快速动态变化,这使得从DRAM迁移至NVM的"冷"页面可能在短时间内变"热"从而产生大量冗余的迁移操作.当前的相关研究都仅着眼于正在执行迁移的页面而忽视了等待迁移和完成迁移的页面,且判断"冷""热"程度的标准不一,使得冗余的迁移大量产生.因此,提出了一个基于DRAM牺牲Cache的异构内存页迁移机制(VC-HMM),使用非易失性存储器中工艺较为成熟的相变存储器(phase change memory, PCM),通过在DRAM和PCM之间增加一个由DRAM构成的小容量牺牲Cache将系统主存DRAM中变"冷"的页面迁移到牺牲Cache中,以避免主存页面在短时间内再次变"热"而造成的冗余迁移.同时,还使得迁回PCM的部分页面不需要写回,减少PCM存储单元的写入操作次数,延长PCM的使用寿命.另外,对于不同的工作负载,VC-HMM可以自适应设置迁移操作的参数,增加迁移的合理性.实验结果表明:与其他迁移策略(CoinMigrator, MQRA,THMigrator)相比,VC-HMM平均减少了至少62.97%的PCM写操作次数、22.72%的平均访问时延、38.37%的重复迁移操作以及3.40%的系统能耗.

When massive data access heterogeneous memory systems, memory pages often migrate between DRAM and NVM. However, the traditional memory page migration strategy is difficult to adapt to the rapid dynamic changes among “hot” and “cold” memory pages. The “cold” pages just migrated from DRAM to NVM will become “hot” again, which results in a large number of redundant migrations, as well as false migrations. Previous related researches only focus on pages that are being migrated without paying too much attention to pages that in the migration waiting queue or that have been migrated. Therefore, this paper proposes a heterogeneous memory page migration mechanism based on DRAM-based victim Cache(VC-HMM) by adding a small capacity of victim Cache between DRAM and PCM. The “cold” pages will be migrated from DRAM to victim Cache. DRAM victim Cache can avoid redundant migrations caused by the main memory pages getting hot again in a short time. Meanwhile, some pages do not need to be written back to PCM that can reduce the number of write operations on PCM and extend the lifetime of PCM. In particular, VC-HMM can automatically update the execution parameters of migration for different workloads to increase the rationality of migration. Experimental results show that compared with other migration strategies(CoinMigrator, MQRA, THMigrator), VC-HMM reduces the average number of PCM write operations by 62.97%, the average access latency by 22.72%, the re-migration times by 38.37%, and the energy consumption by 3.40%.