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KEP-2400: Update swap KEP for 1.23 beta #2858

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Sep 8, 2021
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KEP-2400: Update swap KEP for 1.23 beta #2858

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20a8885
Update swap KEP for 1.23 beta
ehashman Aug 12, 2021
18a9bee
Address PRR feedback
ehashman Sep 8, 2021
8277301
Add test plan note for eviction manager/MemoryPressure
ehashman Sep 8, 2021
908266a
Add swap memory to Kubelet stats API
ehashman Sep 8, 2021
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Add swap memory to Kubelet stats API
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@ehashman
ehashman committed Sep 8, 2021
commit 908266a9c45cafcb7ffdc5b81c60228f7c8fb59a
3 changes: 3 additions & 0 deletions keps/sig-node/2400-node-swap/README.md
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Expand Up @@ -430,6 +430,7 @@ For beta:
detects on the host.
- Consider introducing new configuration modes for swap, such as a node-wide
swap limit for workloads.
- Add swap memory to the Kubelet stats api.
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@ehashman ehashman Sep 8, 2021 •
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@derekwaynecarr suggested this addition for beta.

@dashpole WDYT?

See also #2858 (comment)

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That makes sense to me. I don't remember what swap metrics are available for cgroups v1 vs v2, but I'd want to at least be able to tell if swap is causing problems at the node level. It may also be nice to have swap metrics at the pod/container level if the available metrics can tell me if swapping is hurting my application's performance in some way.

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@dashpole cgroup v2 has memory.swap.current which exists on non-root cgroups which is total amount of swap currently being used by the cgroup and its descendants.

It appears to already be supported in cAdvisor, we just did not include it in k8s API for MemoryStats as it was not yet supported to be on.

see: https://github.com/google/cadvisor/blob/ef7e64f9efab1257e297d7af339e94bb016cf221/container/libcontainer/handler.go#L800

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Looks like cgroups v1 has an equivalent, so we should be all set in that regard

- Determine a set of metrics for node QoS in order to evaluate the performance
of nodes with and without swap enabled.
- Better understand relationship of swap with memory QoS in cgroup v2
Expand Down Expand Up @@ -668,6 +669,8 @@ metrics that can be used to generally quantify node performance.
This section to be updated before the feature can be marked as graduated, and
to be worked on during 1.23 development.

We will also add swap memory utilization to the Kubelet stats API, to provide a means of monitoring this beyond cadvisor Prometheus stats.

- [ ] Metrics
- Metric name:
- [Optional] Aggregation method:
Expand Down