Adding support for /proc/buddyinfo for linux free memory fragmentation.

/prod/buddyinfo returns data on the free blocks fragments available
for use from the kernel.  This data is useful when diagnosing
possible memory fragmentation.

More info can be found in:
* https://lwn.net/Articles/7868/
* https://andorian.blogspot.com/2014/03/making-sense-of-procbuddyinfo.html

collector/buddyinfo.go

@@ -0,0 +1,114 @@
+// 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 !nobuddyinfo
+// +build !windows,!netbsd
+
+package collector
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"strconv"
+	"strings"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/common/log"
+)
+
+type buddyInfo map[string]map[string][]float64
+
+const (
+	buddyInfoSubsystem = "buddyinfo"
+)
+
+type buddyinfoCollector struct {
+	desc *prometheus.Desc
+}
+
+func init() {
+	Factories["buddyinfo"] = NewBuddyinfoCollector
+}
+
+// NewBuddyinfoCollector returns a new Collector exposing buddyinfo stats.
+func NewBuddyinfoCollector() (Collector, error) {
+	desc := prometheus.NewDesc(
+		prometheus.BuildFQName(Namespace, buddyInfoSubsystem, "count"),
+		"Count of free blocks according to size.",
+		[]string{"node", "zone", "size"}, nil,
+	)
+	return &buddyinfoCollector{desc}, nil
+}
+
+// Update calls (*buddyinfoCollector).getBuddyInfo to get the platform specific
+// buddyinfo metrics.
+func (c *buddyinfoCollector) Update(ch chan<- prometheus.Metric) (err error) {
+	buddyInfo, err := c.getBuddyInfo()
+	if err != nil {
+		return fmt.Errorf("couldn't get buddyinfo: %s", err)
+	}
+	log.Debugf("Set node_buddy: %#v", buddyInfo)
+	for node, zones := range buddyInfo {
+		for zone, values := range zones {
+			for size, value := range values {
+				ch <- prometheus.MustNewConstMetric(
+					c.desc,
+					prometheus.GaugeValue, value,
+					node, zone, strconv.Itoa(size),
+				)
+			}
+		}
+	}
+	return nil
+}
+func (c *buddyinfoCollector) getBuddyInfo() (buddyInfo, error) {
+	file, err := os.Open(procFilePath("buddyinfo"))
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+
+	return parseBuddyInfo(file)
+}
+
+func parseBuddyInfo(r io.Reader) (buddyInfo, error) {
+	var (
+		buddyInfo = buddyInfo{}
+		scanner   = bufio.NewScanner(r)
+	)
+
+	for scanner.Scan() {
+		var err error
+		line := scanner.Text()
+		parts := strings.Fields(string(line))
+		node := strings.TrimRight(parts[1], ",")
+		zone := strings.TrimRight(parts[3], ",")
+		arraySize := len(parts[4:])
+		sizes := make([]float64, arraySize)
+		for i := 0; i < arraySize; i++ {
+			sizes[i], err = strconv.ParseFloat(parts[i+4], 64)
+			if err != nil {
+				return nil, fmt.Errorf("invalid value in buddyinfo: %s", err)
+			}
+		}
+
+		if _, ok := buddyInfo[node]; !ok {
+			buddyInfo[node] = make(map[string][]float64)
+		}
+		buddyInfo[node][zone] = sizes
+	}
+
+	return buddyInfo, nil
+}

collector/buddyinfo_test.go

@@ -0,0 +1,40 @@
+// 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.
+
+package collector
+
+import (
+	"os"
+	"testing"
+)
+
+func TestBuddyInfo(t *testing.T) {
+	file, err := os.Open("fixtures/proc/buddyinfo")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer file.Close()
+
+	buddyInfo, err := parseBuddyInfo(file)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if want, got := 4381.0, buddyInfo["0"]["Normal"][0]; want != got {
+		t.Errorf("want Node 0, Zone Normal %f, got %f", want, got)
+	}
+
+	if want, got := 572.0, buddyInfo["0"]["DMA32"][1]; want != got {
+		t.Errorf("want Node 0, Zone DMA32 %f, got %f", want, got)
+	}
+}

collector/fixtures/proc/buddyinfo

@@ -0,0 +1,3 @@
+Node 0, zone      DMA      1      0      1      0      2      1      1      0      1      1      3 
+Node 0, zone    DMA32    759    572    791    475    194     45     12      0      0      0      0 
+Node 0, zone   Normal   4381   1093    185   1530    567    102      4      0      0      0      0