Tuning Linux Swap for Kubernetes: A Deep Dive

Tuning Linux Swap for Kubernetes: A Deep Dive Introduction to Linux swap Anonymous vs File-backed memory Key kernel parameters for swap tuning Swap tests and results Test setup Test methodology Findings Risks and recommendations Kubernetes context Recommended starting point The Kubernetes NodeSwap feature , likely to graduate to stable in the upcoming Kubernetes v1.34 release, allows swap usage: a significant shift from the conventional practice of disabling swap for performance predictability. This article focuses exclusively on tuning swap on Linux nodes, where this feature is available. By allowing Linux nodes to use secondary storage for additional virtual memory when physical RAM is exhausted, node swap support aims to improve resource utilization and reduce out-of-memory (OOM) kills. However, enabling swap is not a "turn-key" solution. The performance and stability of your nodes under memory pressure are critically dependent on a set of Linux kernel parameters. Misconfiguration can lead to performance degradation and interfere with Kubelet's eviction logic. In this blogpost, I'll dive into critical Linux kernel parameters that govern swap behavior. I will explore how these parameters influence Kubernetes workload performance, swap utilization, and crucial eviction mechanisms. I will present various test results showcasing the impact of different configurations, and share my findings on achieving optimal settings for stable and high-performing Kubernetes clusters. At a high level, the Linux kernel manages memory through pages, typically 4KiB in size. When physical memory becomes constrained, the kernel's page replacement algorithm decides which pages to move to swap space. While the exact logic is a sophisticated optimization, this decision-making process is influenced by certain key factors: Page access patterns (how recently pages are accessed) Page dirtyness (whether pages have been modified) Memory pressure (how urgently the system needs free memory) It is important to understand that not all memory pages are the same.