ADT: Aggressive Demotion and Promotion for Tiered Memory

Abstract

Tiered memory using DRAM as upper-tier (fast memory) and emerging slower-but-larger byte-addressable memory as lower-tier (slow memory) is a promising approach to expanding main-memory capacity. Based on the observation that there are many cold pages in data-center applications, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">proactive demotion</i> schemes demote cold pages to slow memory even when free space in fast memory is not deficient. Prior works on proactive demotion lower the requirement of expensive fast-memory capacity by reducing applications' resident set size in fast memory. Also, some of the prior works mitigate the massive performance drop due to insufficient fast-memory capacity when there is a spike in demand for hot data. However, there is room for further improvement to save a larger fast-memory capacity with further aggressive demotion, which can fully reap the aforementioned advantages of proactive demotion. In this paper, we propose a new proactive demotion scheme, ADT, which performs <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</b> ggressive <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</b> emotion and promotion for <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</b> iered memory. Using the memory access locality within the unit in which applications and memory allocators allocate memory, ADT extends the unit of demotion/promotion from the page adopted by prior works to make its demotion more aggressive. By performing demotion and promotion by the extended unit, ADT reduces 29% of fast-memory usage with only a 2.3% performance drop. Also, it achieves 2.28× speedup compared to the default Linux kernel when the system's memory usage is larger than fast-memory capacity, which outperforms state-of-the-art schemes for tiered memory management.