Towards Workload-Aware Page Cache Replacement Policies for Hybrid Memories

Die-stacked DRAM is an emerging technology that is expected to be integrated in future systems with off-package memories resulting in a hybrid memory system. A large body of recent research has investigated the use of die-stacked dynamic random-access memory (DRAM) as a hardware-manged last-level cache. This approach comes at the costs of managing large tag arrays, increased hit latencies, and potentially significant increases in hardware verification costs. An alternative approach is for the operating system (OS) to manage the die-stacked DRAM as a page cache for off-package memories. However, recent work in OS-managed page cache focuses on FIFO replacement and related variants as the baseline management policy. In this paper, we take a step back and investigate classical OS page replacement policies and re-evaluate them for hybrid memories. We find that when we use different die-stacked DRAM sizes, the choice of best management policy depends on cache size and application, and can result in as much as a 13X performance difference. Furthermore, within a single application run, the choice of best policy varies over time. We also evaluate co-scheduled workload pairs and find that the best policy varies by workload pair and cache configuration, and that the best-performing policy is typically the most fair. Our research motivates us to continue our investigation for developing workload-aware and cache configuration-aware page cache management policies.