APMigration: Improving Performance of Hybrid Memory Performance via An Adaptive Page Migration Method

Byte-addressable, non-volatile memory (NVRAM) combines the benefits of DRAM and flash memory. However, due to its slower speed than DRAM, it is best to deploy it in combination with typical DRAM. In such Hybrid NVRAM systems, frequently accessed, hot pages can be stored in DRAM while other cold pages can reside in NVRAM, providing the benefits of both high performance (from DRAM) and lower power consumption and cost/performance (from NVRAM). While the idea seems beneficial, realizing an efficient hybrid NVRAM system requires careful page migration and accurate data temperature measurement. Existing solutions, however, often cause invalid migrations due to inaccurate data temperature accounting, because hot and cold pages are separately identified in DRAM and NVRAM regions. Moreover, since a new NVRAM frame is always allocated for each page swapped back NVRAM, a large amount of unnecessary NVRAM writes are generated during each page migration. Based on these observations, we propose APMigrate, an adaptive data migration approach for hybrid NVRAM systems. APMigrate consist of two parts, UIMigrate and LazyWriteback . UIMigrate focuses on eliminating invalid page migrations by considering data temperature in the entire DRAM-NVRAM space, while LazyWriteback focus on rewriting only dirty data back when the page is swapped back to NVRAM. Our experiments using SPEC 2006 show that APMigrate can reduce the number of migrations and improves performance by up to 90 percent compared to existing state-of-the-art approaches. For some workloads, LazyWriteback can reduce unnecessary NVRAM writes for existing page migrations by up to 75 percent.