cgroupv2: fix swap accounting

[bobrik]

Since runsc v1.0.0-rc94 stats.MemoryStats.SwapUsage on cgroupv2 includes memory usage:

• opencontainers/runc@b99ca25ad0f

This results in wrong metrics:

container_memory_rss{id="/system.slice/qs-dnsv2.service"} 9.173716992e+09 1635890983582
container_memory_swap{id="/system.slice/qs-dnsv2.service"} 1.249011712e+10 1635890983582
container_memory_usage_bytes{id="/system.slice/qs-dnsv2.service"} 1.249011712e+10 1635890983582

Here my service dosn't have any swapped pages, yet it reports all memory as swapped.

[k8s-ci-robot]

Hi @bobrik. Thanks for your PR.

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[bobrik]

I'm not really sure if it's something that needs to be fixed or if I'm expected to do the math myself at query time.

[bobrik]

The metric is correct on cgroupv1, so I think the right way is to merge this fix for cgroupv2.

[bobbypage]

/cc @kolyshkin

[bobbypage]

makes sense, LGTM.

/cc @kolyshkin who made the runc change

[kolyshkin]

Yeah this is weird. cgroup v1 reports mem+swap in this field, so we had to make cgroup v2 report the same. Not sure if there's a better way to address this.

The patch LGTM though.

[bobbypage]

Thanks, LGTM!

[bobbypage]

/ok-to-test

[bobbypage]

/retest