Efficient Memory Tiering in a Virtual Machine

Introduction

Memory tiering is the norm to effectively tackle the increasing server memory total cost of ownership (TCO) and the growing data demands of modern data center workloads. However, the host-based state-of-the-art memory tiering solutions can be inefficient for a virtualized environment when (i) the frequently accessed data are scattered across the guest physical address space or (ii) the accesses to a huge page inside the guest are skewed due to a small number of subpages being hot. Scattered or skewed accesses make the whole huge page look hot in the host address space. This results in host selecting and placing sparsely accessed huge pages in near memory, wasting costly near memory resources. We propose a host-agnostic technique employed inside the guest that exploits the two-level address translation in a virtualized environment to consolidate the scattered and skewed accesses to a set of guest physical address ranges. Consolidation transforms sparsely hot huge pages to densely hot huge pages in the host address space context. As a consequence, host-based tiering solutions can place densely hot huge pages in near memory, improving near memory utilization. Our evaluation of our technique on standalone real-world benchmarks with state-of-the-art host-based tiering show 50-70% reduction in near memory consumption at similar performance levels, while evaluation at scale improves performance by 10-13% with similar memory TCO.