Add counters for memory events.

Also ensure an event is emitted at startup.

PiperOrigin-RevId: 224372065
Change-Id: I5f642b6d6b13c6468ee8f794effe285fcbbf29cf

pkg/sentry/kernel/memevent/BUILD

@@ -12,6 +12,7 @@ go_library(
         ":memory_events_go_proto",
         "//pkg/eventchannel",
         "//pkg/log",
+        "//pkg/metric",
         "//pkg/sentry/kernel",
         "//pkg/sentry/usage",
     ],

pkg/sentry/kernel/memevent/memory_events.go

@@ -22,11 +22,15 @@ import (
 
 	"gvisor.googlesource.com/gvisor/pkg/eventchannel"
 	"gvisor.googlesource.com/gvisor/pkg/log"
+	"gvisor.googlesource.com/gvisor/pkg/metric"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel"
 	pb "gvisor.googlesource.com/gvisor/pkg/sentry/kernel/memevent/memory_events_go_proto"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/usage"
 )
 
+var totalTicks = metric.MustCreateNewUint64Metric("/memory_events/ticks", false /*sync*/, "Total number of memory event periods that have elapsed since startup.")
+var totalEvents = metric.MustCreateNewUint64Metric("/memory_events/events", false /*sync*/, "Total number of memory events emitted.")
+
 // MemoryEvents describes the configuration for the global memory event emitter.
 type MemoryEvents struct {
 	k *kernel.Kernel
@@ -71,6 +75,10 @@ func (m *MemoryEvents) Start() {
 func (m *MemoryEvents) run() {
 	m.done.Add(1)
 
+	// Emit the first event immediately on startup.
+	totalTicks.Increment()
+	m.emit()
+
 	ticker := time.NewTicker(m.period)
 	defer ticker.Stop()
 
@@ -80,6 +88,7 @@ func (m *MemoryEvents) run() {
 			m.done.Done()
 			return
 		case <-ticker.C:
+			totalTicks.Increment()
 			m.emit()
 		}
 	}
@@ -94,6 +103,7 @@ func (m *MemoryEvents) emit() {
 	snapshot, _ := usage.MemoryAccounting.Copy()
 	total := totalPlatform + snapshot.Mapped
 
+	totalEvents.Increment()
 	eventchannel.Emit(&pb.MemoryUsageEvent{
 		Mapped: snapshot.Mapped,
 		Total:  total,