Non-volatile main memory management methods based on a file system

Abstract

There are upcoming non-volatile (NV) memory technologies that provide byte addressability and high performance. PCM, MRAM, and STT-RAM are such examples. Such NV memory can be used as storage because of its data persistency without power supply while it can be used as main memory because of its high performance that matches up with DRAM. There are a number of researches that investigated its uses for main memory and storage. They were, however, conducted independently. This paper presents the methods that enables the integration of the main memory and file system management for NV memory. Such integration makes NV memory simultaneously utilized as both main memory and storage. The presented methods use a file system as their basis for the NV memory management. We implemented the proposed methods in the Linux kernel, and performed the evaluation on the QEMU system emulator. The evaluation results show that 1) the proposed methods can perform comparably to the existing DRAM memory allocator and significantly better than the page swapping, 2) their performance is affected by the internal data structures of a file system, and 3) the data structures appropriate for traditional hard disk drives do not always work effectively for byte addressable NV memory. We also performed the evaluation of the effects caused by the longer access latency of NV memory by cycle-accurate full-system simulation. The results show that the effect on page allocation cost is limited if the increase of latency is moderate.

Non-Volatile Memory File Systems: A Survey

“…Therefore, working with data storage in NVM may take the advantage of using different approaches and methods that systems designed to work with HDDs do not support. Moreover, since the advent of NAND flash memories, the use of NVM as a single layer of memory, merging today's concepts of main memory and back storage, has been proposed [98], [99], aiming to replace the whole memory hierarchy as we know. Such change in the computer architecture would certainly represent a huge shift on software development as well, since most applications and operating systems are designed to store persistent data in the form of files in a secondary memory and to swap this data between layers of faster but volatile memories.…”