app/vmagent/remotewrite: expose metrics with the current number of active series per day and per hour

These numbers are exposed via the following metrics:

- vmagent_hourly_series_limit_current_series
- vmagent_daily_series_limit_current_series

Expose also the limits via the following metrics:

- vmagent_hourly_series_limit_max_series
- vmagent_daily_series_limit_max_series

app/vmagent/remotewrite/remotewrite.go

@@ -81,9 +81,21 @@ func Init() {
 	}
 	if *maxHourlySeries > 0 {
 		hourlySeriesLimiter = bloomfilter.NewLimiter(*maxHourlySeries, time.Hour)
+		_ = metrics.NewGauge(`vmagent_hourly_series_limit_max_series`, func() float64 {
+			return float64(hourlySeriesLimiter.MaxItems())
+		})
+		_ = metrics.NewGauge(`vmagent_hourly_series_limit_current_series`, func() float64 {
+			return float64(hourlySeriesLimiter.CurrentItems())
+		})
 	}
 	if *maxDailySeries > 0 {
 		dailySeriesLimiter = bloomfilter.NewLimiter(*maxDailySeries, 24*time.Hour)
+		_ = metrics.NewGauge(`vmagent_daily_series_limit_max_series`, func() float64 {
+			return float64(dailySeriesLimiter.MaxItems())
+		})
+		_ = metrics.NewGauge(`vmagent_daily_series_limit_current_series`, func() float64 {
+			return float64(dailySeriesLimiter.CurrentItems())
+		})
 	}
 	if *queues > maxQueues {
 		*queues = maxQueues

lib/bloomfilter/limiter.go

@@ -33,6 +33,13 @@ func (l *Limiter) MaxItems() int {
 	return l.maxItems
 }
 
+// CurrentItems return the current number of items registered in l.
+func (l *Limiter) CurrentItems() int {
+	lm := l.v.Load().(*limiter)
+	n := atomic.LoadUint64(&lm.currentItems)
+	return int(n)
+}
+
 // Add adds h to the limiter.
 //
 // It is safe calling Add from concurrent goroutines.