A Study of Memory Placement on Hardware-Assisted Tiered Memory Systems

Recent advances in memory technology, memory hierarchy is becoming diverse with performance-differentiated memory such as high bandwidth memory (HBM) and non-volatile memory (NVM) in modern computer systems. However, the current memory placement has been designed with the assumption that all the memory has the same capabilities based on DRAM. In this letter, we analyze memory placement schemes in state-of-the-art Linux systems to the hardware-assisted tiered memory system. Our analysis is conducted on the real system equipped with Intel's Optane Persistent Memory, enabling tiered memory with DRAM (fast) and Optane (slow) memory. We observe that tiered memory augmented on traditional NUMA form do not exhibit that accessing the local memory provides better performance than that of the remote memory because local Optane memory is slower than remote DRAM. Due to this distinct characteristic, there are several inefficiencies in the commodity operating systems. To make use of tiered memory systems efficiently, this paper explores the design space of practical software solutions, which can be currently applicable in the Linux system.