High `kswapd0` CPU under memory pressure on aws-k8s-1.35+

Author: SparksssjCreated Aug 27, 2026Updated Aug 27, 2026

Labelstype/bugtype/enhancementstatus/needs-triage

Summary of the issue

The issue mostly happens on small instances, and can present as:

kswapd0 becomes the largest CPU consumer. It reached 91.7% CPU in our reproduction.
The node shows high system CPU and I/O wait. Our reproduction showed 59.2% system CPU and 21.5% I/O wait.
Kubernetes becomes stuck launching pods, with pods remaining in ContainerCreating.
Pods fail to start or respond promptly, including readiness probe failures.
The node becomes NotReady.

Workaround

For node groups where Bottlerocket user data can be configured, zram can be disabled during boot with a bootstrap container:

toml

[settings.bootstrap-containers.configure-noswap]
mode = "always"
essential = true
user-data = "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"

This runs the following script:

bash

#!/bin/bash
set -eux
exec 1>&2

ROOTFS="/.bottlerocket/rootfs"
ZRAMCTL="/usr/sbin/zramctl"

if [ ! -s "${ROOTFS}/${ZRAMCTL}" ]; then
  cp /usr/sbin/zramctl "${ROOTFS}"/local
  ZRAMCTL="/local/zramctl"
fi

chroot "${ROOTFS}" swapoff /dev/zram0
chroot "${ROOTFS}" "${ZRAMCTL}" -r /dev/zram0
chroot "${ROOTFS}" modprobe -r zram

In the reproduction above, removing the zram device returned CPU usage to normal while memory usage remained high.

Related issues

Source: bottlerocket-os/bottlerocket

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