Merge pull request #42435 from dashpole/timestamps_for_fsstats

Automatic merge from submit-queue (batch tested with PRs 42369, 42375, 42397, 42435, 42455)

[Bug Fix]: Avoid evicting more pods than necessary by adding Timestamps for fsstats and ignoring stale stats

Continuation of #33121.  Credit for most of this goes to @sjenning.  I added volume fs timestamps.

**why is this a bug** 
This PR attempts to fix part of https://github.com/kubernetes/kubernetes/issues/31362 which results in multiple pods getting evicted unnecessarily whenever the node runs into resource pressure. This PR reduces the chances of such disruptions by avoiding reacting to old/stale metrics.
Without this PR, kubernetes nodes under resource pressure will cause unnecessary disruptions to user workloads. 
This PR will also help deflake a node e2e test suite.

The eviction manager currently avoids evicting pods if metrics are old.  However, timestamp data is not available for filesystem data, and this causes lots of extra evictions.
See the [inode eviction test flakes](https://k8s-testgrid.appspot.com/google-node#kubelet-flaky-gce-e2e) for examples.
This should probably be treated as a bugfix, as it should help mitigate extra evictions.

cc: @kubernetes/sig-storage-pr-reviews  @kubernetes/sig-node-pr-reviews @vishh @derekwaynecarr @sjenning

pkg/volume/volume.go

@@ -26,6 +26,7 @@ import (
 
 	"github.com/golang/glog"
 	"k8s.io/apimachinery/pkg/api/resource"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/types"
 	"k8s.io/kubernetes/pkg/api/v1"
 )
@@ -52,6 +53,9 @@ type MetricsProvider interface {
 
 // Metrics represents the used and available bytes of the Volume.
 type Metrics struct {
+	// The time at which these stats were updated.
+	Time metav1.Time
+
 	// Used represents the total bytes used by the Volume.
 	// Note: For block devices this maybe more than the total size of the files.
 	Used *resource.Quantity