Concurrent page migration for mobile systems with OS-managed hybrid memory

Abstract

Mobile systems are executing applications with increasingly large memory footprints on more processor cores. New execution paradigms for quickly suspending and resuming an application have also become common. Energy consumption remains a paramount concern. Consequently, phase-change memory (PCM) has been suggested for main memory to increase capacity, provide non-volatility for suspend/resume and decrease energy consumption. Because it has limitations for writes, a large PCM is often used along with a small DRAM for good performance. The two memory types may be managed by the operating system, which selects where to allocate pages and schedules background migrations between memory types to move data. To ensure correctness, an application that writes to a migrating page must be paused until the migration completes. Because PCM has long write latency, this situation happens frequently in hybrid memory, leading to long pauses that hurt application responsiveness and performance. This paper describes concurrent page migration (CPM) to alleviate the pauses by buffering writes to migrating pages through the last-level cache. CPM improves performance by up to 22% for single-programmed workloads (17% average) and 13% for multi-programmed workloads (8% average). The technique also preserves the energy and non-volatility benefits of hybrid main memory.