perf: pre-allocate slices

Signed-off-by: Ben Reedy <breed808@breed808.com>

.golangci.yaml

@@ -8,6 +8,7 @@ linters:
   - loggercheck
   - nilnil
   - nilerr
+  - prealloc
   - revive
   - unconvert
   - unparam

pkg/collector/collector.go

@@ -163,11 +163,12 @@ func (c *Collectors) SetPerfCounterQuery() error {
 	var (
 		err error
 
-		perfCounterDependencies []string
-		perfCounterNames        []string
-		perfIndicies            []string
+		perfCounterNames []string
+		perfIndicies     []string
 	)
 
+	perfCounterDependencies := make([]string, 0, len(c.collectors))
+
 	for _, collector := range c.collectors {
 		perfCounterNames, err = collector.GetPerfCounter()
 		if err != nil {

pkg/collector/dfsr/dfsr.go

@@ -130,8 +130,9 @@ func (c *collector) SetLogger(logger log.Logger) {
 
 func (c *collector) GetPerfCounter() ([]string, error) {
 	// Perflib sources are dynamic, depending on the enabled child collectors
-	var perflibDependencies []string
-	for _, source := range utils.ExpandEnabledChildCollectors(*c.dfsrEnabledCollectors) {
+	expandedChildCollectors := utils.ExpandEnabledChildCollectors(*c.dfsrEnabledCollectors)
+	perflibDependencies := make([]string, 0, len(expandedChildCollectors))
+	for _, source := range expandedChildCollectors {
 		perflibDependencies = append(perflibDependencies, dfsrGetPerfObjectName(source))
 	}
 

pkg/collector/textfile/textfile.go

@@ -373,7 +373,7 @@ func scrapeFile(path string, log log.Logger) ([]*dto.MetricFamily, error) {
 	}
 
 	// Use temporary array to check for duplicates
-	var families_array []*dto.MetricFamily
+	families_array := make([]*dto.MetricFamily, 0, len(parsedFamilies))
 
 	for _, mf := range parsedFamilies {
 		families_array = append(families_array, mf)