Bringing number of syscalls down in fs.getDistStatsMap()

fs/fs.go

@@ -19,8 +19,9 @@
 package fs
 
 import (
-	"bufio"
+	"bytes"
 	"fmt"
+	"io"
 	"os"
 	"os/exec"
 	"path"
@@ -58,6 +59,9 @@ const (
 // A pool for restricting the number of consecutive `du` and `find` tasks running.
 var pool = make(chan struct{}, maxConcurrentOps)
 
+// bufSize control size of read buffer in getDiskStatsMap()
+var bufSize = 5000
+
 func init() {
 	for i := 0; i < maxConcurrentOps; i++ {
 		releaseToken()
@@ -504,67 +508,100 @@ func getDiskStatsMap(diskStatsFile string) (map[string]DiskStats, error) {
 	}
 
 	defer file.Close()
-	scanner := bufio.NewScanner(file)
 
-	for scanner.Scan() {
-		line := scanner.Text()
-		words := strings.Fields(line)
-		if !partitionRegex.MatchString(words[2]) {
-			continue
+	leftover := []byte{}
+	const newline = 10
+	for {
+		buf := make([]byte, bufSize)
+		count, err := file.Read(buf)
+		buf = append(leftover, bytes.Trim(buf, "\x00")...)
+		klog.V(10).Infof("read %d bytes in getDiskStatsMap()", count)
+		if err == io.EOF {
+			break
+		}
+		lines := bytes.Split(buf, []byte{newline})
+		var skipLastLine bool
+		if buf[len(buf)-1] != newline {
+			skipLastLine = true
 		}
-		// 8      50 sdd2 40 0 280 223 7 0 22 108 0 330 330
-		deviceName := path.Join("/dev", words[2])
 
-		var err error
-		devInfo := make([]uint64, 2)
-		for i := 0; i < len(devInfo); i++ {
-			devInfo[i], err = strconv.ParseUint(words[i], 10, 64)
+		for i, bLine := range lines {
+			if len(bLine) == 0 {
+				klog.V(10).Infof("skipping empty line in getDiskStatsMap() iteration %d", i)
+				continue
+			}
+			if skipLastLine && i == len(lines)-1 {
+				klog.V(10).Infof("skipping leftover line in getDiskStatsMap() iteration %d", i)
+				continue
+			}
+			line := string(bLine)
+			words := strings.Fields(line)
+
+			if !partitionRegex.MatchString(words[2]) {
+				continue
+			}
+			// 8      50 sdd2 40 0 280 223 7 0 22 108 0 330 330
+			deviceName := path.Join("/dev", words[2])
+
+			var err error
+			devInfo := make([]uint64, 2)
+			for i := 0; i < len(devInfo); i++ {
+				devInfo[i], err = strconv.ParseUint(words[i], 10, 64)
+				if err != nil {
+					return nil, err
+				}
+			}
+
+			wordLength := len(words)
+			offset := 3
+			var stats = make([]uint64, wordLength-offset)
+			if len(stats) < 11 {
+				return nil, fmt.Errorf("could not parse all 11 columns of /proc/diskstats")
+			}
+			for i := offset; i < wordLength; i++ {
+				stats[i-offset], err = strconv.ParseUint(words[i], 10, 64)
+				if err != nil {
+					return nil, err
+				}
+			}
+
+			major64, err := strconv.ParseUint(words[0], 10, 64)
 			if err != nil {
 				return nil, err
 			}
-		}
 
-		wordLength := len(words)
-		offset := 3
-		var stats = make([]uint64, wordLength-offset)
-		if len(stats) < 11 {
-			return nil, fmt.Errorf("could not parse all 11 columns of /proc/diskstats")
-		}
-		for i := offset; i < wordLength; i++ {
-			stats[i-offset], err = strconv.ParseUint(words[i], 10, 64)
+			minor64, err := strconv.ParseUint(words[1], 10, 64)
 			if err != nil {
 				return nil, err
 			}
+
+			diskStats := DiskStats{
+				MajorNum:        devInfo[0],
+				MinorNum:        devInfo[1],
+				ReadsCompleted:  stats[0],
+				ReadsMerged:     stats[1],
+				SectorsRead:     stats[2],
+				ReadTime:        stats[3],
+				WritesCompleted: stats[4],
+				WritesMerged:    stats[5],
+				SectorsWritten:  stats[6],
+				WriteTime:       stats[7],
+				IoInProgress:    stats[8],
+				IoTime:          stats[9],
+				WeightedIoTime:  stats[10],
+				Major:           major64,
+				Minor:           minor64,
+			}
+			diskStatsMap[deviceName] = diskStats
 		}
 
-		major64, err := strconv.ParseUint(words[0], 10, 64)
-		if err != nil {
-			return nil, err
+		if buf[len(buf)-1] != newline {
+			leftover = lines[len(lines)-1]
+			klog.V(10).Info("saving leftover line %q", leftover)
+		} else {
+			leftover = []byte{}
 		}
 
-		minor64, err := strconv.ParseUint(words[1], 10, 64)
-		if err != nil {
-			return nil, err
-		}
-
-		diskStats := DiskStats{
-			MajorNum:        devInfo[0],
-			MinorNum:        devInfo[1],
-			ReadsCompleted:  stats[0],
-			ReadsMerged:     stats[1],
-			SectorsRead:     stats[2],
-			ReadTime:        stats[3],
-			WritesCompleted: stats[4],
-			WritesMerged:    stats[5],
-			SectorsWritten:  stats[6],
-			WriteTime:       stats[7],
-			IoInProgress:    stats[8],
-			IoTime:          stats[9],
-			WeightedIoTime:  stats[10],
-			Major:           major64,
-			Minor:           minor64,
-		}
-		diskStatsMap[deviceName] = diskStats
 	}
 	return diskStatsMap, nil
 }

fs/fs_test.go

@@ -40,6 +40,9 @@ func TestMountInfoFromDir(t *testing.T) {
 }
 
 func TestGetDiskStatsMap(t *testing.T) {
+	origBufSize := bufSize
+	bufSize = 100
+	defer func() { bufSize = origBufSize }()
 	diskStatsMap, err := getDiskStatsMap("test_resources/diskstats")
 	if err != nil {
 		t.Errorf("Error calling getDiskStatsMap %s", err)
@@ -92,6 +95,9 @@ func TestGetDiskStatsMap(t *testing.T) {
 }
 
 func TestGetDiskStatsMapMajorMinorNum(t *testing.T) {
+	origBufSize := bufSize
+	bufSize = 100
+	defer func() { bufSize = origBufSize }()
 	diskStatsMap, err := getDiskStatsMap("test_resources/diskstats")
 	if err != nil {
 		t.Errorf("Error calling getDiskStatsMap %s", err)
@@ -108,6 +114,9 @@ func TestGetDiskStatsMapMajorMinorNum(t *testing.T) {
 }
 
 func TestFileNotExist(t *testing.T) {
+	origBufSize := bufSize
+	bufSize = 100
+	defer func() { bufSize = origBufSize }()
 	_, err := getDiskStatsMap("/file_does_not_exist")
 	if err != nil {
 		t.Fatalf("getDiskStatsMap must not error for absent file: %s", err)