bcache: add priorityStats flag (#1621)

* bcache: add priorityStats flag

Fixes #1593

Signed-off-by: Aleksei Zakharov <zaharov@selectel.ru>

collector/bcache_linux.go

@@ -21,6 +21,11 @@ import (
 	"github.com/go-kit/kit/log"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/procfs/bcache"
+	"gopkg.in/alecthomas/kingpin.v2"
+)
+
+var (
+	priorityStats = kingpin.Flag("collector.bcache.priorityStats", "Expose expensive priority stats.").Bool()
 )
 
 func init() {
@@ -50,7 +55,13 @@ func NewBcacheCollector(logger log.Logger) (Collector, error) {
 // Update reads and exposes bcache stats.
 // It implements the Collector interface.
 func (c *bcacheCollector) Update(ch chan<- prometheus.Metric) error {
-	stats, err := c.fs.Stats()
+	var stats []*bcache.Stats
+	var err error
+	if *priorityStats {
+		stats, err = c.fs.Stats()
+	} else {
+		stats, err = c.fs.StatsWithoutPriority()
+	}
 	if err != nil {
 		return fmt.Errorf("failed to retrieve bcache stats: %w", err)
 	}
@@ -259,7 +270,10 @@ func (c *bcacheCollector) updateBcacheStats(ch chan<- prometheus.Metric, s *bcac
 				extraLabel:      []string{"cache_device"},
 				extraLabelValue: cache.Name,
 			},
+		}
+		if *priorityStats {
 			// metrics in /sys/fs/bcache/<uuid>/<cache>/priority_stats
+			priorityStatsMetrics := []bcacheMetric{
 				{
 					name:            "priority_stats_unused_percent",
 					desc:            "The percentage of the cache that doesn't contain any data.",
@@ -277,6 +291,8 @@ func (c *bcacheCollector) updateBcacheStats(ch chan<- prometheus.Metric, s *bcac
 					extraLabelValue: cache.Name,
 				},
 			}
+			metrics = append(metrics, priorityStatsMetrics...)
+		}
 		allMetrics = append(allMetrics, metrics...)
 	}
 

end-to-end-test.sh

@@ -106,6 +106,7 @@ fi
   --collector.wifi.fixtures="collector/fixtures/wifi" \
   --collector.qdisc.fixtures="collector/fixtures/qdisc/" \
   --collector.netclass.ignored-devices="(bond0|dmz|int)" \
+  --collector.bcache.priorityStats \
   --collector.cpu.info \
   --collector.cpu.info.flags-include="^(aes|avx.?|constant_tsc)$" \
   --collector.cpu.info.bugs-include="^(cpu_meltdown|spectre_.*|mds)$" \