Allocation Policies Matter for Hybrid Memory Systems

Existing tiered memory systems all use DRAM-Preferred as their allocation policy, whereby pages get allocated from higher-performing DRAM until it is filled, after which all future allocations are made from lower-performing persistent memory (PM). The novel insight of this work is that the right page allocation policy for a workload can help to lower the access latencies for the newly allocated pages. We design, implement, and evaluate three page allocation policies within the real system deployment of the state-of-the-art dynamic tiering system. We observe that the right page allocation policy can improve the performance of a tiered memory system by as much as 17x for certain workloads.