Compressed swap and an early memory-pressure response address different problems. Their proposed CoreOS defaults do not make Kubernetes memory limits disappear.
A Fedora 45 change, not proof about every node
The accepted CoreOS change targets Fedora 45 and plans systemd-oomd with swap on zram for existing and new installations. A release proposal does not establish the configuration of a running node: inspect its deployed version, stream and local overrides.
Zram holds compressed data in RAM. In our deliberately simplified example, four GiB of pages compress to two GiB, freeing about two GiB before metadata and other overhead. It does not add four GiB of physical memory. Poorly compressible pages offer less relief, and compression/decompression consumes CPU time.
The termination policy is another layer
The systemd-oomd manual describes cgroup-v2 and pressure monitoring. Configured ManagedOOM policies select eligible descendant cgroups for termination; enabling the service alone does not mean every unit is a target. oomctl displays monitored groups and pressure information.
That action is distinct from a container exceeding its memory limit and from kubelet eviction. When diagnosing a restart, collect the container reason and host logs before naming the killer. A compressed-swap device does not cancel the other policies.
Kubernetes asks two separate questions
The Kubernetes swap guide distinguishes failSwapOn: false, which lets kubelet start with swap present, from memorySwap.swapBehavior. The default NoSwap prevents Pod workloads from swapping; processes outside those containers can still use host swap. LimitedSwap permits eligible workloads under limits, rather than offering unrestricted extra memory.
Our cover separates physical compression, kubelet admission to a swap-enabled host, and workload policy. Before a node rollout, reproduce memory pressure on a test node using the same runtime and configuration. Observe application latency as well as survival: avoiding an immediate termination is not useful if the service becomes too slow to meet its purpose.
September 8: distinguish accepted Fedora 45 plan, compressed RAM and cgroup policy; explain the separate kubelet swap settings.