Update some change tracker doc comments

In particular, fix the description of ServiceChangeTracker.Update's
return value, and point out that it's different from
EndpointsChangeTracker.EndpointSliceUpdate's (though fortunately, in a
way that doesn't matter for any existing code).

pkg/proxy/endpointschangetracker.go

@@ -40,23 +40,25 @@ type EndpointsChangeTracker struct {
 	// lock protects lastChangeTriggerTimes
 	lock sync.Mutex
 
+	// processEndpointsMapChange is invoked by the apply function on every change.
+	// This function should not modify the EndpointsMaps, but just use the changes for
+	// any Proxier-specific cleanup.
 	processEndpointsMapChange processEndpointsMapChangeFunc
+
 	// endpointSliceCache holds a simplified version of endpoint slices.
 	endpointSliceCache *EndpointSliceCache
-	// Map from the Endpoints namespaced-name to the times of the triggers that caused the endpoints
+
-	// object to change. Used to calculate the network-programming-latency.
+	// lastChangeTriggerTimes maps from the Service's NamespacedName to the times of
+	// the triggers that caused its EndpointSlice objects to change. Used to calculate
+	// the network-programming-latency metric.
 	lastChangeTriggerTimes map[types.NamespacedName][]time.Time
-	// record the time when the endpointsChangeTracker was created so we can ignore the endpoints
+	// trackerStartTime is the time when the EndpointsChangeTracker was created, so
-	// that were generated before, because we can't estimate the network-programming-latency on those.
+	// we can avoid generating network-programming-latency metrics for changes that
-	// This is specially problematic on restarts, because we process all the endpoints that may have been
+	// occurred before that.
-	// created hours or days before.
 	trackerStartTime time.Time
 }
 
 type makeEndpointFunc func(info *BaseEndpointInfo, svcPortName *ServicePortName) Endpoint
-
-// This handler is invoked by the apply function on every change. This function should not modify the
-// EndpointsMap's but just use the changes for any Proxier specific cleanup.
 type processEndpointsMapChangeFunc func(oldEndpointsMap, newEndpointsMap EndpointsMap)
 
 // NewEndpointsChangeTracker initializes an EndpointsChangeTracker
@@ -69,9 +71,10 @@ func NewEndpointsChangeTracker(hostname string, makeEndpointInfo makeEndpointFun
 	}
 }
 
-// EndpointSliceUpdate updates given service's endpoints change map based on the <previous, current> endpoints pair.
+// EndpointSliceUpdate updates the EndpointsChangeTracker by adding/updating or removing
-// It returns true if items changed, otherwise return false. Will add/update/delete items of EndpointsChangeTracker.
+// endpointSlice (depending on removeSlice). It returns true if this update contained a
-// If removeSlice is true, slice will be removed, otherwise it will be added or updated.
+// change that needs to be synced; note that this is different from the return value of
+// ServiceChangeTracker.Update().
 func (ect *EndpointsChangeTracker) EndpointSliceUpdate(endpointSlice *discovery.EndpointSlice, removeSlice bool) bool {
 	if !supportedEndpointSliceAddressTypes.Has(string(endpointSlice.AddressType)) {
 		klog.V(4).InfoS("EndpointSlice address type not supported by kube-proxy", "addressType", endpointSlice.AddressType)

pkg/proxy/servicechangetracker.go

@@ -36,18 +36,20 @@ type ServiceChangeTracker struct {
 	lock sync.Mutex
 	// items maps a service to its serviceChange.
 	items map[types.NamespacedName]*serviceChange
-	// makeServiceInfo allows proxier to inject customized information when processing service.
-	makeServiceInfo         makeServicePortFunc
-	processServiceMapChange processServiceMapChangeFunc
-	ipFamily                v1.IPFamily
 
+	// makeServiceInfo allows the proxier to inject customized information when
+	// processing services.
+	makeServiceInfo makeServicePortFunc
+	// processServiceMapChange is invoked by the apply function on every change. This
+	// function should not modify the ServicePortMaps, but just use the changes for
+	// any Proxier-specific cleanup.
+	processServiceMapChange processServiceMapChangeFunc
+
+	ipFamily v1.IPFamily
 	recorder events.EventRecorder
 }
 
 type makeServicePortFunc func(*v1.ServicePort, *v1.Service, *BaseServicePortInfo) ServicePort
-
-// This handler is invoked by the apply function on every change. This function should not modify the
-// ServicePortMap's but just use the changes for any Proxier specific cleanup.
 type processServiceMapChangeFunc func(previous, current ServicePortMap)
 
 // serviceChange contains all changes to services that happened since proxy rules were synced.  For a single object,
@@ -69,16 +71,11 @@ func NewServiceChangeTracker(makeServiceInfo makeServicePortFunc, ipFamily v1.IP
 	}
 }
 
-// Update updates given service's change map based on the <previous, current> service pair.  It returns true if items changed,
+// Update updates the ServiceChangeTracker based on the <previous, current> service pair
-// otherwise return false.  Update can be used to add/update/delete items of ServiceChangeMap.  For example,
+// (where either previous or current, but not both, can be nil). It returns true if sct
-// Add item
+// contains changes that need to be synced (whether or not those changes were caused by
-//   - pass <nil, service> as the <previous, current> pair.
+// this update); note that this is different from the return value of
-//
+// EndpointChangeTracker.EndpointSliceUpdate().
-// Update item
-//   - pass <oldService, service> as the <previous, current> pair.
-//
-// Delete item
-//   - pass <service, nil> as the <previous, current> pair.
 func (sct *ServiceChangeTracker) Update(previous, current *v1.Service) bool {
 	// This is unexpected, we should return false directly.
 	if previous == nil && current == nil {