kubelet: eviction: add memcg threshold notifier to improve eviction responsiveness

pkg/kubelet/eviction/BUILD

@@ -25,6 +25,7 @@ go_library(
         "//pkg/api/unversioned:go_default_library",
         "//pkg/client/record:go_default_library",
         "//pkg/kubelet/api/v1alpha1/stats:go_default_library",
+        "//pkg/kubelet/cm:go_default_library",
         "//pkg/kubelet/lifecycle:go_default_library",
         "//pkg/kubelet/qos:go_default_library",
         "//pkg/kubelet/server/stats:go_default_library",

pkg/kubelet/eviction/eviction_manager.go

@@ -24,7 +24,9 @@ import (
 
 	"github.com/golang/glog"
 	"k8s.io/kubernetes/pkg/api"
+	"k8s.io/kubernetes/pkg/api/resource"
 	"k8s.io/kubernetes/pkg/client/record"
+	"k8s.io/kubernetes/pkg/kubelet/cm"
 	"k8s.io/kubernetes/pkg/kubelet/lifecycle"
 	"k8s.io/kubernetes/pkg/kubelet/qos"
 	"k8s.io/kubernetes/pkg/kubelet/server/stats"
@@ -33,7 +35,7 @@ import (
 	"k8s.io/kubernetes/pkg/util/wait"
 )
 
-// managerImpl implements NodeStabilityManager
+// managerImpl implements Manager
 type managerImpl struct {
 	//  used to track time
 	clock clock.Clock
@@ -65,6 +67,8 @@ type managerImpl struct {
 	resourceToNodeReclaimFuncs map[api.ResourceName]nodeReclaimFuncs
 	// last observations from synchronize
 	lastObservations signalObservations
+	// notifiersInitialized indicates if the threshold notifiers have been initialized (i.e. synchronize() has been called once)
+	notifiersInitialized bool
 }
 
 // ensure it implements the required interface
@@ -139,6 +143,39 @@ func (m *managerImpl) IsUnderDiskPressure() bool {
 	return hasNodeCondition(m.nodeConditions, api.NodeDiskPressure)
 }
 
+func startMemoryThresholdNotifier(thresholds []Threshold, observations signalObservations, hard bool, handler thresholdNotifierHandlerFunc) error {
+	for _, threshold := range thresholds {
+		if threshold.Signal != SignalMemoryAvailable || hard != isHardEvictionThreshold(threshold) {
+			continue
+		}
+		observed, found := observations[SignalMemoryAvailable]
+		if !found {
+			continue
+		}
+		cgroups, err := cm.GetCgroupSubsystems()
+		if err != nil {
+			return err
+		}
+		// TODO add support for eviction from --cgroup-root
+		cgpath, found := cgroups.MountPoints["memory"]
+		if !found || len(cgpath) == 0 {
+			return fmt.Errorf("memory cgroup mount point not found")
+		}
+		attribute := "memory.usage_in_bytes"
+		quantity := getThresholdQuantity(threshold.Value, observed.capacity)
+		usageThreshold := resource.NewQuantity(observed.capacity.Value(), resource.DecimalSI)
+		usageThreshold.Sub(*quantity)
+		description := fmt.Sprintf("<%s available", formatThresholdValue(threshold.Value))
+		memcgThresholdNotifier, err := NewMemCGThresholdNotifier(cgpath, attribute, usageThreshold.String(), description, handler)
+		if err != nil {
+			return err
+		}
+		go memcgThresholdNotifier.Start(wait.NeverStop)
+		return nil
+	}
+	return nil
+}
+
 // synchronize is the main control loop that enforces eviction thresholds.
 func (m *managerImpl) synchronize(diskInfoProvider DiskInfoProvider, podFunc ActivePodsFunc) {
 	// if we have nothing to do, just return
@@ -166,8 +203,27 @@ func (m *managerImpl) synchronize(diskInfoProvider DiskInfoProvider, podFunc Act
 		return
 	}
 
-	// find the list of thresholds that are met independent of grace period
-	now := m.clock.Now()
+	// attempt to create a threshold notifier to improve eviction response time
+	if !m.notifiersInitialized {
+		m.notifiersInitialized = true
+		// start soft memory notification
+		err = startMemoryThresholdNotifier(m.config.Thresholds, observations, false, func(desc string) {
+			glog.Infof("soft memory eviction threshold crossed at %s", desc)
+			// TODO wait grace period for soft memory limit
+			m.synchronize(diskInfoProvider, podFunc)
+		})
+		if err != nil {
+			glog.Warningf("eviction manager: failed to create hard memory threshold notifier: %v", err)
+		}
+		// start hard memory notification
+		err = startMemoryThresholdNotifier(m.config.Thresholds, observations, true, func(desc string) {
+			glog.Infof("hard memory eviction threshold crossed at %s", desc)
+			m.synchronize(diskInfoProvider, podFunc)
+		})
+		if err != nil {
+			glog.Warningf("eviction manager: failed to create soft memory threshold notifier: %v", err)
+		}
+	}
 
 	// determine the set of thresholds met independent of grace period
 	thresholds = thresholdsMet(thresholds, observations, false)
@@ -182,6 +238,7 @@ func (m *managerImpl) synchronize(diskInfoProvider DiskInfoProvider, podFunc Act
 	thresholds = thresholdsUpdatedStats(thresholds, observations, m.lastObservations)
 
 	// track when a threshold was first observed
+	now := m.clock.Now()
 	thresholdsFirstObservedAt := thresholdsFirstObservedAt(thresholds, m.thresholdsFirstObservedAt, now)
 
 	// the set of node conditions that are triggered by currently observed thresholds
@@ -218,7 +275,7 @@ func (m *managerImpl) synchronize(diskInfoProvider DiskInfoProvider, podFunc Act
 	glog.Warningf("eviction manager: attempting to reclaim %v", resourceToReclaim)
 
 	// determine if this is a soft or hard eviction associated with the resource
-	softEviction := isSoftEviction(thresholds, resourceToReclaim)
+	softEviction := isSoftEvictionThresholds(thresholds, resourceToReclaim)
 
 	// record an event about the resources we are now attempting to reclaim via eviction
 	m.recorder.Eventf(m.nodeRef, api.EventTypeWarning, "EvictionThresholdMet", "Attempting to reclaim %s", resourceToReclaim)

pkg/kubelet/eviction/helpers.go

@@ -848,18 +848,23 @@ func getStarvedResources(thresholds []Threshold) []api.ResourceName {
 }
 
 // isSoftEviction returns true if the thresholds met for the starved resource are only soft thresholds
-func isSoftEviction(thresholds []Threshold, starvedResource api.ResourceName) bool {
+func isSoftEvictionThresholds(thresholds []Threshold, starvedResource api.ResourceName) bool {
 	for _, threshold := range thresholds {
 		if resourceToCheck := signalToResource[threshold.Signal]; resourceToCheck != starvedResource {
 			continue
 		}
-		if threshold.GracePeriod == time.Duration(0) {
+		if isHardEvictionThreshold(threshold) {
 			return false
 		}
 	}
 	return true
 }
 
+// isSoftEviction returns true if the thresholds met for the starved resource are only soft thresholds
+func isHardEvictionThreshold(threshold Threshold) bool {
+	return threshold.GracePeriod == time.Duration(0)
+}
+
 // buildResourceToRankFunc returns ranking functions associated with resources
 func buildResourceToRankFunc(withImageFs bool) map[api.ResourceName]rankFunc {
 	resourceToRankFunc := map[api.ResourceName]rankFunc{

pkg/kubelet/eviction/threshold_notifier.go

@@ -0,0 +1,124 @@
+/*
+Copyright 2016 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package eviction
+
+/*
+#include <sys/eventfd.h>
+*/
+import "C"
+
+import (
+	"fmt"
+	"syscall"
+
+	"github.com/golang/glog"
+)
+
+// ThresholdNotifier notifies the user when an attribute crosses a threshold value
+type ThresholdNotifier interface {
+	Start(stopCh <-chan struct{})
+}
+
+type memcgThresholdNotifier struct {
+	watchfd     int
+	controlfd   int
+	eventfd     int
+	handler     thresholdNotifierHandlerFunc
+	description string
+}
+
+var _ ThresholdNotifier = &memcgThresholdNotifier{}
+
+// NewMemCGThresholdNotifier sends notifications when a cgroup threshold
+// is crossed (in either direction) for a given cgroup attribute
+func NewMemCGThresholdNotifier(path, attribute, threshold, description string, handler thresholdNotifierHandlerFunc) (ThresholdNotifier, error) {
+	watchfd, err := syscall.Open(fmt.Sprintf("%s/%s", path, attribute), syscall.O_RDONLY, 0)
+	if err != nil {
+		return nil, err
+	}
+	defer func() {
+		if err != nil {
+			syscall.Close(watchfd)
+		}
+	}()
+	controlfd, err := syscall.Open(fmt.Sprintf("%s/cgroup.event_control", path), syscall.O_WRONLY, 0)
+	if err != nil {
+		return nil, err
+	}
+	defer func() {
+		if err != nil {
+			syscall.Close(controlfd)
+		}
+	}()
+	efd, err := C.eventfd(0, C.EFD_CLOEXEC)
+	if err != nil {
+		return nil, err
+	}
+	eventfd := int(efd)
+	if eventfd < 0 {
+		err = fmt.Errorf("eventfd call failed")
+		return nil, err
+	}
+	defer func() {
+		if err != nil {
+			syscall.Close(eventfd)
+		}
+	}()
+	glog.V(2).Infof("eviction: setting notification threshold to %s", threshold)
+	config := fmt.Sprintf("%d %d %s", eventfd, watchfd, threshold)
+	_, err = syscall.Write(controlfd, []byte(config))
+	if err != nil {
+		return nil, err
+	}
+	return &memcgThresholdNotifier{
+		watchfd:     watchfd,
+		controlfd:   controlfd,
+		eventfd:     eventfd,
+		handler:     handler,
+		description: description,
+	}, nil
+}
+
+func getThresholdEvents(eventfd int, eventCh chan<- int) {
+	for {
+		buf := make([]byte, 8)
+		_, err := syscall.Read(eventfd, buf)
+		if err != nil {
+			return
+		}
+		eventCh <- 0
+	}
+}
+
+func (n *memcgThresholdNotifier) Start(stopCh <-chan struct{}) {
+	eventCh := make(chan int, 1)
+	go getThresholdEvents(n.eventfd, eventCh)
+	for {
+		select {
+		case <-stopCh:
+			glog.V(2).Infof("eviction: stopping threshold notifier")
+			syscall.Close(n.watchfd)
+			syscall.Close(n.controlfd)
+			syscall.Close(n.eventfd)
+			close(eventCh)
+			return
+		case <-eventCh:
+			glog.V(2).Infof("eviction: threshold crossed")
+			n.handler(n.description)
+		}
+	}
+}

pkg/kubelet/eviction/types.go

@@ -161,3 +161,6 @@ type nodeReclaimFunc func() (*resource.Quantity, error)
 
 // nodeReclaimFuncs is an ordered list of nodeReclaimFunc
 type nodeReclaimFuncs []nodeReclaimFunc
+
+// thresholdNotifierHandlerFunc is a function that takes action in response to a crossed threshold
+type thresholdNotifierHandlerFunc func(thresholdDescription string)