feat: add swapOnlyUsage in MemoryStats

[HeRaNO]

implement #4000

[lifubang]

Thanks for your contribution. Please use git rebase main to catch up with the latest update, instead of merge main.

[HeRaNO]

Thanks for your contribution. Please use git rebase main to catch up with the latest update, instead of merge main.

done

[lifubang]

And could you see rootStatsFromMeminfo in

runc/libcontainer/cgroups/fs2/memory.go

Lines 105 to 114 in b137e99

	memoryUsage, err := getMemoryDataV2(dirPath, "")
	if err != nil {
	if errors.Is(err, unix.ENOENT) && dirPath == UnifiedMountpoint {
	// The root cgroup does not have memory.{current,max}
	// so emulate those using data from /proc/meminfo and
	// /sys/fs/cgroup/memory.stat
	return rootStatsFromMeminfo(stats)
	}
	return err
	}

1. Do you know whether .pead exist in UnifiedMountpoint or not?
2. If not, could you know how to get max_usage_in_bytes from /proc/meminfo?

[HeRaNO]

And could you see rootStatsFromMeminfo in

runc/libcontainer/cgroups/fs2/memory.go

Lines 105 to 114 in b137e99

	memoryUsage, err := getMemoryDataV2(dirPath, "")
	if err != nil {
	if errors.Is(err, unix.ENOENT) && dirPath == UnifiedMountpoint {
	// The root cgroup does not have memory.{current,max}
	// so emulate those using data from /proc/meminfo and
	// /sys/fs/cgroup/memory.stat
	return rootStatsFromMeminfo(stats)
	}
	return err
	}

1. Do you know whether .peak exist in UnifiedMountpoint or not?
2. If not, could you know how to get max_usage_in_bytes from /proc/meminfo?

1. No.
2. It seems that /proc/meminfo doesn't export any usage of memory watermark, so It's hard to get max_usage_in_bytes.

[AkihiroSuda]

Can we have a test?

[HeRaNO]

Can we have a test?

Sure, added.

[HeRaNO]

@haircommander @lifubang @AkihiroSuda PTAL, thx

[AkihiroSuda]

Please squash commits

[haircommander]

LGTM

[HeRaNO]

@kolyshkin PTAL, thx

[lifubang]

It seems that we have accepted the ‘swapOnlyUsage’ approach, so please add some descriptions in ‘libcontainer/README.md’ to make each memory stat field more clear to the users.

[HeRaNO]

It seems that we have accepted the ‘swapOnlyUsage’ approach, so please add some descriptions in ‘libcontainer/README.md’ to make each memory stat field more clear to the users.

I've added some explanation in CHANGELOG.md.

[kolyshkin]

Seems reasonable. LGTM

[HeRaNO]

All checks pass now. Ready to merge.