PET: Proactive Demotion for Efficient Tiered Memory Management

초록

Tiered memory is a promising approach for increasing main-memory capacity at a lower cost by using DRAM as the upper tier (fast memory) and slower-but-cheap byte-addressable memory as the lower tier (slow memory). A proactive demotion, one of the ways to use tiered memory efficiently, demotes cold data to slow memory even when fast memory has sufficient free space. Prior works have utilized proactive demotion to reduce the high cost of main memory by reducing applications' resident set size in fast memory. Further, proactive demotion helps mitigate severe performance degradation caused by fast memory shortages when there is a spike in demand for hot data. Still, we observe that leveraging memory access locality within the allocation units of applications enables larger fast-memory savings with lower system overhead. We propose a new proactive demotion scheme, PET, which performs proactive demotion for efficient tiered memory management. PET proposes extending the unit of demotion and promotion from the OS page, adopted by prior works, to PET-block (P-block), which reflects the unit in which applications allocate memory. We also provide the mechanisms that carefully select the demotion target P-block and swiftly promote the demoted P-block when the access pattern changes. The prototype of PET on Linux kernel v6.1.44 reduces 39.8% (up to 80.4%) of fast-memory usage with only a 1.7% performance drop on average of the evaluated workloads. Also, it mitigates 31% performance slowdown 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.

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