Revamping Storage Class Memory With Hardware Automated Memory-Over-Storage Solution

TL;DR

This paper introduces HAMS, a hardware-based solution that combines NVDIMM and ultra-low latency flash into a unified memory system, significantly reducing overheads and improving performance and energy efficiency.

Contribution

The paper presents HAMS, a hardware automated Memory-over-Storage system that integrates NVDIMM and ULL-Flash into a single large memory space with OS transparency, reducing software overheads.

Findings

HAMS achieves 97% higher system performance than software-based hybrid NVDIMM.

Advanced HAMS improves performance by 119% and reduces energy consumption by 45%.

Hardware integration significantly outperforms traditional software-managed memory solutions.

Abstract

Large persistent memories such as NVDIMM have been perceived as a disruptive memory technology, because they can maintain the state of a system even after a power failure and allow the system to recover quickly. However, overheads incurred by a heavy software-stack intervention seriously negate the benefits of such memories. First, to significantly reduce the software stack overheads, we propose HAMS, a hardware automated Memory-over-Storage (MoS) solution. Specifically, HAMS aggregates the capacity of NVDIMM and ultra-low latency flash archives (ULL-Flash) into a single large memory space, which can be used as a working or persistent memory expansion, in an OS-transparent manner. HAMS resides in the memory controller hub and manages its MoS address pool over conventional DDR and NVMe interfaces; it employs a simple hardware cache to serve all the memory requests from the host MMU after mapping the storage space of ULL-Flash to the memory space of NVDIMM. Second, to make HAMS more energy-efficient and reliable, we propose an "advanced HAMS" which removes unnecessary data transfers between NVDIMM and ULL-Flash after optimizing the datapath and hardware modules of HAMS. This approach unleashes the ULL-Flash and its NVMe controller from the storage box and directly connects the HAMS datapath to NVDIMM over the conventional DDR4 interface. Our evaluations show that HAMS and advanced HAMS can offer 97% and 119% higher system performance than a software-based hybrid NVDIMM design, while consuming 41% and 45% lower system energy, respectively.