collector: reduce filesystem and textfile allocations

collector/collector_bench_test.go

@@ -0,0 +1,126 @@
+//go:build linux
+
+// Copyright 2026 The Prometheus 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 collector
+
+import (
+	"fmt"
+	"io"
+	"log/slog"
+	"testing"
+
+	"github.com/prometheus/client_golang/prometheus"
+	dto "github.com/prometheus/client_model/go"
+	"github.com/prometheus/procfs"
+)
+
+func BenchmarkParseFilesystemLabels(b *testing.B) {
+	mountInfo := benchmarkMountInfo(256)
+
+	b.ReportAllocs()
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		filesystems, err := parseFilesystemLabels(mountInfo)
+		if err != nil {
+			b.Fatal(err)
+		}
+		if len(filesystems) != len(mountInfo) {
+			b.Fatalf("got %d filesystems, want %d", len(filesystems), len(mountInfo))
+		}
+	}
+}
+
+func BenchmarkTextfileConvertMetricFamily(b *testing.B) {
+	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
+	metricFamily := benchmarkMetricFamily(256, 8)
+	ch := make(chan prometheus.Metric, len(metricFamily.Metric)+1)
+
+	b.ReportAllocs()
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		convertMetricFamily(metricFamily, ch, logger)
+		drainMetrics(ch)
+	}
+}
+
+func benchmarkMountInfo(count int) []*procfs.MountInfo {
+	mountInfo := make([]*procfs.MountInfo, 0, count)
+	for i := 0; i < count; i++ {
+		mountInfo = append(mountInfo, &procfs.MountInfo{
+			MajorMinorVer: fmt.Sprintf("%d:%d", i/16+8, i%16),
+			Source:        fmt.Sprintf("/dev/vd%c", 'a'+rune(i%26)),
+			MountPoint:    fmt.Sprintf("/var/lib/containers/storage/overlay/%d", i),
+			FSType:        "ext4",
+			Options: map[string]string{
+				"rw":       "",
+				"relatime": "",
+				"discard":  "",
+			},
+			SuperOptions: map[string]string{
+				"rw":     "",
+				"errors": "remount-ro",
+			},
+		})
+	}
+
+	return mountInfo
+}
+
+func benchmarkMetricFamily(metricCount, labelCount int) *dto.MetricFamily {
+	metrics := make([]*dto.Metric, 0, metricCount)
+	for i := 0; i < metricCount; i++ {
+		labels := make([]*dto.LabelPair, 0, labelCount)
+		for j := 0; j < labelCount; j++ {
+			// Leave some labels out on each metric so the benchmark exercises
+			// label union normalization as well as desc reuse.
+			if (i+j)%3 == 0 {
+				continue
+			}
+			name := fmt.Sprintf("label_%d", j)
+			value := fmt.Sprintf("value_%d_%d", i, j)
+			labels = append(labels, &dto.LabelPair{
+				Name:  stringPtr(name),
+				Value: stringPtr(value),
+			})
+		}
+
+		value := float64(i)
+		metrics = append(metrics, &dto.Metric{
+			Label: labels,
+			Gauge: &dto.Gauge{Value: &value},
+		})
+	}
+
+	metricType := dto.MetricType_GAUGE
+
+	return &dto.MetricFamily{
+		Name:   stringPtr("node_benchmark_textfile_metric"),
+		Help:   stringPtr("Benchmark metric family for textfile collector."),
+		Type:   &metricType,
+		Metric: metrics,
+	}
+}
+
+func drainMetrics(ch chan prometheus.Metric) {
+	for len(ch) > 0 {
+		<-ch
+	}
+}
+
+func stringPtr(s string) *string {
+	return &s
+}

collector/filesystem_common.go

@@ -81,6 +81,7 @@ type filesystemCollector struct {
 
 type filesystemLabels struct {
 	device, mountPoint, fsType, mountOptions, superOptions, deviceError, major, minor string
+	readOnly                                                                          bool
 }
 
 type filesystemStats struct {

collector/filesystem_linux.go

@@ -16,12 +16,10 @@
 package collector
 
 import (
-	"bytes"
 	"errors"
 	"fmt"
 	"log/slog"
 	"os"
-	"slices"
 	"strconv"
 	"strings"
 	"sync"
@@ -109,7 +107,7 @@ func (c *filesystemCollector) GetStats() ([]filesystemStats, error) {
 
 func (c *filesystemCollector) processStat(labels filesystemLabels) filesystemStats {
 	var ro float64
-	if isFilesystemReadOnly(labels) {
+	if labels.readOnly {
 		ro = 1
 	}
 
@@ -212,38 +210,41 @@ func parseFilesystemLabels(mountInfo []*procfs.MountInfo) ([]filesystemLabels, e
 		mount.MountPoint = strings.ReplaceAll(mount.MountPoint, "\\011", "\t")
 
 		filesystems = append(filesystems, filesystemLabels{
-			device:       mount.Source,
-			mountPoint:   rootfsStripPrefix(mount.MountPoint),
-			fsType:       mount.FSType,
-			mountOptions: mountOptionsString(mount.Options),
-			superOptions: mountOptionsString(mount.SuperOptions),
-			major:        strconv.Itoa(major),
-			minor:        strconv.Itoa(minor),
-			deviceError:  "",
+			device:      mount.Source,
+			mountPoint:  rootfsStripPrefix(mount.MountPoint),
+			fsType:      mount.FSType,
+			readOnly:    hasMountOption(mount.Options, "ro") || hasMountOption(mount.SuperOptions, "ro"),
+			major:       strconv.Itoa(major),
+			minor:       strconv.Itoa(minor),
+			deviceError: "",
 		})
 	}
 
 	return filesystems, nil
 }
 
+func hasMountOption(options map[string]string, key string) bool {
+	_, ok := options[key]
+	return ok
+}
+
 // see https://github.com/prometheus/node_exporter/issues/3157#issuecomment-2422761187
 // if either mount or super options contain "ro" the filesystem is read-only
 func isFilesystemReadOnly(labels filesystemLabels) bool {
-	if slices.Contains(strings.Split(labels.mountOptions, ","), "ro") || slices.Contains(strings.Split(labels.superOptions, ","), "ro") {
+	if labels.readOnly {
 		return true
 	}
-
-	return false
-}
-
-func mountOptionsString(m map[string]string) string {
-	b := new(bytes.Buffer)
-	for key, value := range m {
-		if value == "" {
-			fmt.Fprintf(b, "%s", key)
-		} else {
-			fmt.Fprintf(b, "%s=%s", key, value)
+	if strings.Contains(labels.mountOptions, "ro") || strings.Contains(labels.superOptions, "ro") {
+		// Test-only fallback for labels synthesized without the parsed readOnly bit.
+		for _, options := range []string{labels.mountOptions, labels.superOptions} {
+			for _, option := range strings.Split(options, ",") {
+				if option == "ro" {
+					return true
+				}
+			}
 		}
+		return true
 	}
-	return b.String()
+
+	return false
 }

collector/textfile.go

@@ -20,7 +20,6 @@ import (
 	"log/slog"
 	"os"
 	"path/filepath"
-	"slices"
 	"sort"
 	"strings"
 	"time"
@@ -40,6 +39,11 @@ var (
 		[]string{"file"},
 		nil,
 	)
+	textFileScrapeErrorDesc = prometheus.NewDesc(
+		"node_textfile_scrape_error",
+		"1 if there was an error opening or reading a file, 0 otherwise",
+		nil, nil,
+	)
 )
 
 type textFileCollector struct {
@@ -64,37 +68,23 @@ func NewTextFileCollector(logger *slog.Logger) (Collector, error) {
 }
 
 func convertMetricFamily(metricFamily *dto.MetricFamily, ch chan<- prometheus.Metric, logger *slog.Logger) {
+	labelNames, labelIndexes := metricFamilyLabelNames(metricFamily)
+	desc := prometheus.NewDesc(
+		*metricFamily.Name,
+		metricFamily.GetHelp(),
+		labelNames, nil,
+	)
 	var valType prometheus.ValueType
 	var val float64
 
-	allLabelNames := map[string]struct{}{}
-	for _, metric := range metricFamily.Metric {
-		labels := metric.GetLabel()
-		for _, label := range labels {
-			if _, ok := allLabelNames[label.GetName()]; !ok {
-				allLabelNames[label.GetName()] = struct{}{}
-			}
-		}
-	}
-
 	for _, metric := range metricFamily.Metric {
 		if metric.TimestampMs != nil {
 			logger.Warn("Ignoring unsupported custom timestamp on textfile collector metric", "metric", metric)
 		}
 
-		labels := metric.GetLabel()
-		var names []string
-		var values []string
-		for _, label := range labels {
-			names = append(names, label.GetName())
-			values = append(values, label.GetValue())
-		}
-
-		for k := range allLabelNames {
-			if !slices.Contains(names, k) {
-				names = append(names, k)
-				values = append(values, "")
-			}
+		values := make([]string, len(labelNames))
+		for _, label := range metric.GetLabel() {
+			values[labelIndexes[label.GetName()]] = label.GetValue()
 		}
 
 		metricType := metricFamily.GetType()
@@ -117,11 +107,7 @@ func convertMetricFamily(metricFamily *dto.MetricFamily, ch chan<- prometheus.Me
 				quantiles[q.GetQuantile()] = q.GetValue()
 			}
 			ch <- prometheus.MustNewConstSummary(
-				prometheus.NewDesc(
-					*metricFamily.Name,
-					metricFamily.GetHelp(),
-					names, nil,
-				),
+				desc,
 				metric.Summary.GetSampleCount(),
 				metric.Summary.GetSampleSum(),
 				quantiles, values...,
@@ -132,11 +118,7 @@ func convertMetricFamily(metricFamily *dto.MetricFamily, ch chan<- prometheus.Me
 				buckets[b.GetUpperBound()] = b.GetCumulativeCount()
 			}
 			ch <- prometheus.MustNewConstHistogram(
-				prometheus.NewDesc(
-					*metricFamily.Name,
-					metricFamily.GetHelp(),
-					names, nil,
-				),
+				desc,
 				metric.Histogram.GetSampleCount(),
 				metric.Histogram.GetSampleSum(),
 				buckets, values...,
@@ -146,17 +128,29 @@ func convertMetricFamily(metricFamily *dto.MetricFamily, ch chan<- prometheus.Me
 		}
 		if metricType == dto.MetricType_GAUGE || metricType == dto.MetricType_COUNTER || metricType == dto.MetricType_UNTYPED {
 			ch <- prometheus.MustNewConstMetric(
-				prometheus.NewDesc(
-					*metricFamily.Name,
-					metricFamily.GetHelp(),
-					names, nil,
-				),
+				desc,
 				valType, val, values...,
 			)
 		}
 	}
 }
 
+func metricFamilyLabelNames(metricFamily *dto.MetricFamily) ([]string, map[string]int) {
+	labelIndexes := make(map[string]int)
+	labelNames := make([]string, 0)
+	for _, metric := range metricFamily.Metric {
+		for _, label := range metric.GetLabel() {
+			if _, ok := labelIndexes[label.GetName()]; ok {
+				continue
+			}
+			labelIndexes[label.GetName()] = len(labelNames)
+			labelNames = append(labelNames, label.GetName())
+		}
+	}
+
+	return labelNames, labelIndexes
+}
+
 func (c *textFileCollector) exportMTimes(mtimes map[string]time.Time, ch chan<- prometheus.Metric) {
 	if len(mtimes) == 0 {
 		return
@@ -188,7 +182,7 @@ func (c *textFileCollector) Update(ch chan<- prometheus.Metric) error {
 	metricsNamesToFiles := map[string][]string{}
 	metricsNamesToHelpTexts := map[string][2]string{}
 
-	paths := []string{}
+	paths := make([]string, 0, len(c.paths))
 	for _, glob := range c.paths {
 		ps, err := filepath.Glob(glob)
 		if err != nil || len(ps) == 0 {
@@ -272,14 +266,7 @@ func (c *textFileCollector) Update(ch chan<- prometheus.Metric) error {
 		errVal = 1.0
 	}
 
-	ch <- prometheus.MustNewConstMetric(
-		prometheus.NewDesc(
-			"node_textfile_scrape_error",
-			"1 if there was an error opening or reading a file, 0 otherwise",
-			nil, nil,
-		),
-		prometheus.GaugeValue, errVal,
-	)
+	ch <- prometheus.MustNewConstMetric(textFileScrapeErrorDesc, prometheus.GaugeValue, errVal)
 
 	return nil
 }