S-Tiering: A Unified HW/SW Solution for Memory Tiering Based on the Standard CXL Hotness Monitoring Unit

In this paper, we proposeS-Tiering, a unified hardware and software solution for memory tiering based on the standard CXL Hotness Monitoring Unit (CHMU).S-Tieringconsists of hardware components that comply with CHMU hardware specification defined in the CXL 3.2 Specification, and software components that control hardware components. Based on these components,S-Tieringminimizes the access to CXL memory by properly steering page migration.We evaluate various probabilistic data structure algorithms and adopt a Count-Min Sketch-based Hot Page Tracker that achieves 99% accuracy with only 0.3% tracking buffer overhead compared to assigning a dedicated counter for every 4KB page. We implement hardware components ofS-Tieringon an Field-Programmable Gate Array board and software components ofS-Tieringon Ubuntu 22.04 with Linux-v6.8 kernel. We evaluate the performance impact ofS-Tieringon benchmarks representative of real applications (e.g., High Performance Computing, Graph-processing, In-Memory Database).S-Tieringachieves a performance improvement of up to 193% compared to first-touch allocation and outperforms AutoNUMA memory tiering by 184%p.S-Tieringminimizes the memory access to CXL memory and increases the bandwidth utilization of DDR memory up to ×11.