Footprint-Based DIMM Hotplug

Power-efficiency has become one of the most critical concerns for HPC as we continue to scale computational capabilities. A significant fraction of system power is spent on large main memories, mainly caused by the substantial amount of DIMM standby power needed. However, while necessary for some workloads, for many workloads large memory configurations are too rich, i.e., these workloads only make use of a fraction of the available memory, causing unnecessary power usage. This observation opens new opportunities for power reduction by powering DIMMs on and off depending on the current workload. In this article, we propose footprint-based DIMM hotplug that enables a compute node to adjust the number of DIMMs that are powered on depending on the memory footprint of a running job. Our technique relies on two main subcomponents-memory footprint monitoring and DIMM management-which we both implement as part of an optimized page management system with small control overhead. Using Linux's memory hotplug capabilities, we implement our approach on a real system, and our results show that our proposed technique can save 50.6-52.1 percent of the DIMM standby energy and the CPU+DRAM energy of up to 1.50 Wh for various small-memory-footprint applications without loss of performance.