metric/system: preallocate arrays

Whenever possible, preallocate array to the correct size instead of letting arrays "grow". This reduces the load on the Garbage Collector and improves memory usage efficiency. Signed-off-by: Florian Lehner <[email protected]>
elastic · Nov 20, 2023 · cbbccb6 · cbbccb6
1 parent c117bd8
commit cbbccb6
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Showing 5 changed files with 11 additions and 11 deletions.
diff --git a/metric/system/diskio/diskstat_windows_helper.go b/metric/system/diskio/diskstat_windows_helper.go
@@ -59,7 +59,7 @@ func ioCounters(names ...string) (map[string]disk.IOCountersStat, error) {
 	if err != nil || len(logicalDisks) == 0 {
 		return nil, err
 	}
-	ret := make(map[string]disk.IOCountersStat)
+	ret := make(map[string]disk.IOCountersStat, len(logicalDisks))
 	for _, drive := range logicalDisks {
 		// not get _Total or Harddrive
 		if len(drive.Name) > 3 {
@@ -158,7 +158,7 @@ func getLogicalDriveStrings() ([]logicalDrive, error) {
 		}
 		return nil, err
 	}
-	var logicalDrives []logicalDrive
+	logicalDrives := make([]logicalDrive, 0, len(lpBuffer))
 	for _, v := range lpBuffer {
 		if v >= 65 && v <= 90 {
 			s := string(v)

diff --git a/metric/system/process/process.go b/metric/system/process/process.go
@@ -115,8 +115,8 @@ func (procStats *Stats) Get() ([]mapstr.M, []mapstr.M, error) {
 	}
 
 	// Format the list to the MapStr type used by the outputs
-	var procs []mapstr.M
-	var rootEvents []mapstr.M
+	procs := make([]mapstr.M, 0, len(plist))
+	rootEvents := make([]mapstr.M, 0, len(plist))
 
 	for _, process := range plist {
 		process := process

diff --git a/metric/system/process/process_darwin.go b/metric/system/process/process_darwin.go
@@ -64,8 +64,8 @@ func (procStats *Stats) FetchPids() (ProcsMap, []ProcState, error) {
 
 	bbuf := bytes.NewBuffer(buf)
 
-	procMap := make(ProcsMap, 0)
-	var plist []ProcState
+	procMap := make(ProcsMap, num)
+	plist := make([]ProcState, 0, num)
 
 	for i := 0; i < num; i++ {
 		if err := binary.Read(bbuf, binary.LittleEndian, &pid); err != nil {
@@ -193,7 +193,7 @@ func getProcArgs(pid int, filter func(string) bool) ([]string, string, mapstr.M,
 	}
 
 	// read CLI args
-	var argv []string
+	argv := make([]string, 0, argc)
 	for i := 0; i < int(argc); i++ {
 		arg, err := bbuf.ReadBytes(0)
 		if err == io.EOF {

diff --git a/metric/system/process/process_linux_common.go b/metric/system/process/process_linux_common.go
@@ -58,8 +58,8 @@ func (procStats *Stats) FetchPids() (ProcsMap, []ProcState, error) {
 		return nil, nil, fmt.Errorf("error reading directory names: %w", err)
 	}
 
-	procMap := make(ProcsMap)
-	var plist []ProcState
+	procMap := make(ProcsMap, len(names))
+	plist := make([]ProcState, 0, len(names))
 
 	// Iterate over the directory, fetch just enough info so we can filter based on user input.
 	logger := logp.L()

diff --git a/metric/system/process/process_windows.go b/metric/system/process/process_windows.go
@@ -38,8 +38,8 @@ func (procStats *Stats) FetchPids() (ProcsMap, []ProcState, error) {
 		return nil, nil, fmt.Errorf("EnumProcesses failed: %w", err)
 	}
 
-	procMap := make(ProcsMap, 0)
-	var plist []ProcState
+	procMap := make(ProcsMap, len(pids))
+	plist := make([]ProcState, 0, len(pids))
 	// This is probably the only implementation that doesn't benefit from our
 	// little fillPid callback system. We'll need to iterate over everything
 	// manually.