To reduce the lock pressure on the kernfs file system, we should reduce the frequency of cgroup reads.

[xigang]

Intro:
We call cadvisor subcontainers API to obtain the data of all cgroup containers. With the increase of QPS, the frequency of cgroup read will increase, which will aggravate the pressure of kernfs file system lock and even cause machine hang.

Question:
Do we need to read the cgroup less frequently when we call GetInfo to fetch ContainerInfo data by caching it?

https://github.com/google/cadvisor/blob/54dff2b8ccb147747d814b0ff3b4a3256dc569c0/manager/manager.go#L543C19-L543C47

func (m *manager) containerDataToContainerInfo(cont *containerData, query *info.ContainerInfoRequest) (*info.ContainerInfo, error) {
	// Get the info from the container.
	cinfo, err := cont.GetInfo(true)  
	if err != nil {
		return nil, err
	}

	stats, err := m.memoryCache.RecentStats(cinfo.Name, query.Start, query.End, query.NumStats)
	if err != nil {
		return nil, err
	}

	// Make a copy of the info for the user.
	ret := &info.ContainerInfo{
		ContainerReference: cinfo.ContainerReference,
		Subcontainers:      cinfo.Subcontainers,
		Spec:               m.getAdjustedSpec(cinfo),
		Stats:              stats,
	}
	return ret, nil
}

If the call GetInfo (shouldUpdateSubcontainers bool) function shouldUpdateSubcontainers parameter is set to true, The updateSpec() function is called on each request to read the cgroup data, which increases the pressure on kernsfs Lock.

func (cd *containerData) GetInfo(shouldUpdateSubcontainers bool) (*containerInfo, error) {
	// Get spec and subcontainers.
	if cd.clock.Since(cd.infoLastUpdatedTime) > 5*time.Second || shouldUpdateSubcontainers {
		err := cd.updateSpec()
		if err != nil {
			return nil, err
		}
		if shouldUpdateSubcontainers {
			err = cd.updateSubcontainers()
			if err != nil {
				return nil, err
			}
		}
		cd.infoLastUpdatedTime = cd.clock.Now()
	}
	cd.lock.Lock()
	defer cd.lock.Unlock()
	cInfo := containerInfo{
		Subcontainers: cd.info.Subcontainers,
		Spec:          cd.info.Spec,
	}
	cInfo.Id = cd.info.Id
	cInfo.Name = cd.info.Name
	cInfo.Aliases = cd.info.Aliases
	cInfo.Namespace = cd.info.Namespace
	return &cInfo, nil
}