nuKSM: NUMA-aware Memory De-duplication for Multi-socket Servers

Abstract

An operating system's memory management has multiple goals, e.g. reducing memory access latencies, reducing memory footprint. These goals can conflict with each other when independent subsystems optimize them in silos.

In this work, we report one such conflict that appears between memory de-duplication and NUMA management. Linux's memory de-duplication subsystem, namely KSM, is NUMA unaware. Consequently, while de-duplicating pages across NUMA nodes, it can place de-duplicated pages in a manner that can lead to significant performance variations, unfairness, and subvert process priority.

We introduce NUMA-aware KSM, a.k.a., nuKSM, that makes judicious decisions about the placement of de-duplicated pages to reduce the impact of NUMA and unfairness in execution. nuKSM also enables users to avoid priority subversion. Finally, independent of the NUMA effect, we observed that KSM fails to scale well to large memory systems due to its centralized design. We thus extended nuKSM to adopt a de-centralized design to scale to larger memory sizes.