reduce memory alloc of append

cpu_linux.go

@@ -9,10 +9,11 @@ import (
 )
 
 func CPUTimes(percpu bool) ([]CPUTimesStat, error) {
-	var ret []CPUTimesStat
-
 	filename := "/proc/stat"
 	lines, _ := readLines(filename)
+
+	ret := make([]CPUTimesStat, 0, len(lines))
+
 	for _, line := range lines {
 		ct, err := parseStatLine(line)
 		if err != nil {

disk_freebsd.go

@@ -17,7 +17,7 @@ func DiskPartitions(all bool) ([]DiskPartitionStat, error) {
 		return ret, err
 	}
 
-	fs := make([]Statfs, count)
+	fs := make([]Statfs, 0, count)
 	_, err = Getfsstat(fs, MNT_WAIT)
 
 	for _, stat := range fs {

disk_linux.go

@@ -14,14 +14,15 @@ const (
 // Get disk partitions.
 // should use setmntent(3) but this implement use /etc/mtab file
 func DiskPartitions(all bool) ([]DiskPartitionStat, error) {
-	var ret []DiskPartitionStat
 
 	filename := "/etc/mtab"
 	lines, err := readLines(filename)
 	if err != nil {
-		return ret, err
+		return nil, err
 	}
 
+	ret := make([]DiskPartitionStat, 0, len(lines))
+
 	for _, line := range lines {
 		fields := strings.Fields(line)
 		d := DiskPartitionStat{
@@ -36,15 +37,13 @@ func DiskPartitions(all bool) ([]DiskPartitionStat, error) {
 }
 
 func DiskIOCounters() (map[string]DiskIOCountersStat, error) {
-	ret := make(map[string]DiskIOCountersStat, 0)
-
 	// determine partitions we want to look for
 	filename := "/proc/partitions"
 	lines, err := readLines(filename)
 	if err != nil {
-		return ret, err
+		return nil, err
 	}
-	var partitions []string
+	partitions := make([]string, 0, len(lines)-2)
 
 	for _, line := range lines[2:] {
 		fields := strings.Fields(line)
@@ -64,8 +63,9 @@ func DiskIOCounters() (map[string]DiskIOCountersStat, error) {
 	filename = "/proc/diskstats"
 	lines, err = readLines(filename)
 	if err != nil {
-		return ret, err
+		return nil, err
 	}
+	ret := make(map[string]DiskIOCountersStat, 0)
 	for _, line := range lines {
 		fields := strings.Fields(line)
 		name := fields[2]

host_linux.go

@@ -33,22 +33,23 @@ func BootTime() (int64, error) {
 
 func Users() ([]UserStat, error) {
 	utmpfile := "/var/run/utmp"
-	var ret []UserStat
 
 	file, err := os.Open(utmpfile)
 	if err != nil {
-		return ret, err
+		return nil, err
 	}
 
 	buf, err := ioutil.ReadAll(file)
 	if err != nil {
-		return ret, err
+		return nil, err
 	}
 
 	u := utmp{}
 	entrySize := int(unsafe.Sizeof(u))
 	count := len(buf) / entrySize
 
+	ret := make([]UserStat, 0, count)
+
 	for i := 0; i < count; i++ {
 		b := buf[i*entrySize : i*entrySize+entrySize]