Add new collector exposing 'ksmd' stats

Add new collector which exposes the content of /sys/kernel/mm/ksm
directory. This directory contains control and statistics files for
Kernel Samepage Merging daemon.

The collector is not enabled by default.

Signed-off-by: Pavel Borzenkov <pavel.borzenkov@gmail.com>

collector/fixtures/e2e-output.txt

@@ -444,6 +444,33 @@ node_forks 26442
 # HELP node_intr Total number of interrupts serviced.
 # TYPE node_intr counter
 node_intr 8.885917e+06
+# HELP node_ksmd_full_scans_total ksmd 'full_scans' file.
+# TYPE node_ksmd_full_scans_total counter
+node_ksmd_full_scans_total 323
+# HELP node_ksmd_merge_across_nodes ksmd 'merge_across_nodes' file.
+# TYPE node_ksmd_merge_across_nodes gauge
+node_ksmd_merge_across_nodes 1
+# HELP node_ksmd_pages_shared ksmd 'pages_shared' file.
+# TYPE node_ksmd_pages_shared gauge
+node_ksmd_pages_shared 1
+# HELP node_ksmd_pages_sharing ksmd 'pages_sharing' file.
+# TYPE node_ksmd_pages_sharing gauge
+node_ksmd_pages_sharing 255
+# HELP node_ksmd_pages_to_scan ksmd 'pages_to_scan' file.
+# TYPE node_ksmd_pages_to_scan gauge
+node_ksmd_pages_to_scan 100
+# HELP node_ksmd_pages_unshared ksmd 'pages_unshared' file.
+# TYPE node_ksmd_pages_unshared gauge
+node_ksmd_pages_unshared 0
+# HELP node_ksmd_pages_volatile ksmd 'pages_volatile' file.
+# TYPE node_ksmd_pages_volatile gauge
+node_ksmd_pages_volatile 0
+# HELP node_ksmd_run ksmd 'run' file.
+# TYPE node_ksmd_run gauge
+node_ksmd_run 1
+# HELP node_ksmd_sleep_seconds ksmd 'sleep_millisecs' file.
+# TYPE node_ksmd_sleep_seconds gauge
+node_ksmd_sleep_seconds 0.02
 # HELP node_load1 1m load average.
 # TYPE node_load1 gauge
 node_load1 0.21

collector/fixtures/sys/kernel/mm/ksm/full_scans

@@ -0,0 +1 @@
+323

collector/fixtures/sys/kernel/mm/ksm/merge_across_nodes

@@ -0,0 +1 @@
+1

collector/fixtures/sys/kernel/mm/ksm/pages_shared

@@ -0,0 +1 @@
+1

collector/fixtures/sys/kernel/mm/ksm/pages_sharing

@@ -0,0 +1 @@
+255

collector/fixtures/sys/kernel/mm/ksm/pages_to_scan

@@ -0,0 +1 @@
+100

collector/fixtures/sys/kernel/mm/ksm/pages_unshared

@@ -0,0 +1 @@
+0

collector/fixtures/sys/kernel/mm/ksm/pages_volatile

@@ -0,0 +1 @@
+0

collector/fixtures/sys/kernel/mm/ksm/run

@@ -0,0 +1 @@
+1

collector/fixtures/sys/kernel/mm/ksm/sleep_millisecs

@@ -0,0 +1 @@
+20

collector/ksmd_linux.go

@@ -0,0 +1,83 @@
+// Copyright 2015 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.
+
+// +build !noksmd
+
+package collector
+
+import (
+	"fmt"
+	"path"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+var (
+	ksmdFiles = []string{"full_scans", "merge_across_nodes", "pages_shared", "pages_sharing",
+		"pages_to_scan", "pages_unshared", "pages_volatile", "run", "sleep_millisecs"}
+)
+
+type ksmdCollector struct {
+	metricDescs map[string]*prometheus.Desc
+}
+
+func init() {
+	Factories["ksmd"] = NewKsmdCollector
+}
+
+func getCanonicalMetricName(filename string) string {
+	switch filename {
+	case "full_scans":
+		return filename + "_total"
+	case "sleep_millisecs":
+		return "sleep_seconds"
+	default:
+		return filename
+	}
+}
+
+// Takes a prometheus registry and returns a new Collector exposing
+// kernel/system statistics.
+func NewKsmdCollector() (Collector, error) {
+	subsystem := "ksmd"
+	descs := make(map[string]*prometheus.Desc)
+
+	for _, n := range ksmdFiles {
+		descs[n] = prometheus.NewDesc(
+			prometheus.BuildFQName(Namespace, subsystem, getCanonicalMetricName(n)),
+			fmt.Sprintf("ksmd '%s' file.", n), nil, nil)
+	}
+	return &ksmdCollector{descs}, nil
+}
+
+// Expose kernel and system statistics.
+func (c *ksmdCollector) Update(ch chan<- prometheus.Metric) (err error) {
+	for _, n := range ksmdFiles {
+		val, err := readUintFromFile(sysFilePath(path.Join("kernel/mm/ksm", n)))
+		if err != nil {
+			return err
+		}
+
+		t := prometheus.GaugeValue
+		v := float64(val)
+		switch n {
+		case "full_scans":
+			t = prometheus.CounterValue
+		case "sleep_millisecs":
+			v /= 1000
+		}
+		ch <- prometheus.MustNewConstMetric(c.metricDescs[n], t, v)
+	}
+
+	return nil
+}

end-to-end-test.sh

@@ -7,6 +7,7 @@ collectors=$(cat << COLLECTORS
   diskstats
   entropy
   filefd
+  ksmd
   loadavg
   mdadm
   meminfo