MOCA: Memory Object Classification and Allocation in Heterogeneous Memory Systems

Abstract

In the era of abundant-data computing, main memory's latency and power significantly impact overall system performance and power. Today's computing systems are typically composed of homogeneous memory modules, which are optimized to provide either low latency, high bandwidth, or low power. Such memory modules do not cater to a wide range of applications with diverse memory access behavior. Thus, heterogeneous memory systems, which include several memory modules with distinct performance and power characteristics, are becoming promising alternatives. In such a system, allocating applications to their best-fitting memory modules improves system performance and energy efficiency. However, such an approach still leaves the full potential of heterogeneous memory systems under-utilized because not only applications, but also the memory objects within that application differ in their memory access behavior. This paper proposes a novel page allocation approach to utilize heterogeneous memory systems at the memory object level. We design a memory object classification and allocation framework (MOCA) to characterize memory objects and then allocate them to their best-fit memory module to improve performance and energy efficiency. We experiment with heterogeneous memory systems that are composed of a Reduced Latency DRAM (RLDRAM) for latency-sensitive objects, a 2.5D-stacked High Bandwidth Memory (HBM) for bandwidth-sensitive objects, and a Low Power DDR (LPDDR) for non-memory-intensive objects. The MOCA framework includes detailed application profiling, a classification mechanism, and an allocation policy to place memory objects. Compared to a system with homogeneous memory modules, we demonstrate that heterogeneous memory systems with MOCA improve memory system energy efficiency by up to 63%. Compared to a heterogeneous memory system with only application-level page allocation, MOCA achieves a 26% memory performance and a 33% energy efficiency improvement for multi-program workloads.