Tierce: Observability-Driven Tiered Memory Management for Colocated Workloads

Tiered memory systems rely on hardware signals to estimate page criticality and decide which pages should remain in fast memory. Colocation corrupts these estimates at two points: shared LLC interference changes whether accesses reach memory, and downstream memory contention changes their stall cost. Both effects blend colocated workloads' behavior into shared page-criticality estimates, creating a fundamental observability gap for tiered memory management.

We present Tierce, an observability substrate for colocated tiered memory. Tierce estimates workload-local exposed stall by measuring per-workload memory-level parallelism and scoring pages by realized access latency. It bounds LLC interference with explicit cache-way allocation. Across 8 colocated pairs that run four foreground workloads against a bandwidth-intensive and a bursty, phase-varying co-runner, Tierce outperforms PACT, the best prior art, on every pair, by 2.2% to 12.6%.