Hisui: Unlocking Tiered Memory Efficiency for FaaS Workloads

Modern tiered-memory architectures are increasingly adopted in cloud servers with extensive physical capacity. Realizing their full performance potential, however, requires effective page management. Existing systems, tuned for long-running workloads, primarily rely on access-count-based promotion. Yet this policy is ill-suited to the short-lived, event-driven model of Function-as-a-Service (FaaS) workloads. The resulting workload-architecture mismatch yields poor page placement and severely degrades architectural efficiency. We present Hisui, a FaaS-aware tiered-memory management system tailored to FaaS workloads. It stages pages with high expected reuse using two mechanisms: an FMem admission filter and an invocation-frequency-weighted valuation that promotes pages by descending gain. Hisui delivers up to 1.57× higher throughput than access-count baselines and consistently lowers latency on real workloads.