Avoid array growth in FilteredList.

The method (*schedulerCache).FilteredList builds an array of *v1.Pod that contains every pod in the cluster except for those filtered out by a predicate. Today, it starts with a nil slice and appends to it. Based on current usage, FilteredList is expected to return every pod in the cluster or omit some pods from a single node. This change reserves array capacity equal to the total number of pods in the cluster.

Avoid array growth in FilteredList.
3909dc13 · Jonathan Basseri · 8bd5a460 · 3909dc13
Commit 3909dc13 authored Dec 19, 2017 by Jonathan Basseri
Hide whitespace changes
Inline Side-by-side

Showing with 8 additions and 1 deletion

cache.go plugin/pkg/scheduler/schedulercache/cache.go +8 -1

No files found.
--- a/plugin/pkg/scheduler/schedulercache/cache.go
+++ b/plugin/pkg/scheduler/schedulercache/cache.go
@@ -104,7 +104,14 @@ func (cache *schedulerCache) List(selector labels.Selector) ([]*v1.Pod, error) {
 func (cache *schedulerCache) FilteredList(podFilter PodFilter, selector labels.Selector) ([]*v1.Pod, error) {
 	cache.mu.Lock()
 	defer cache.mu.Unlock()
-	var pods []*v1.Pod
+	// podFilter is expected to return true for most or all of the pods. We
+	// can avoid expensive array growth without wasting too much memory by
+	// pre-allocating capacity.
+	maxSize := 0
+	for _, info := range cache.nodes {
+		maxSize += len(info.pods)
+	}
+	pods := make([]*v1.Pod, 0, maxSize)
 	for _, info := range cache.nodes {
 		for _, pod := range info.pods {
 			if podFilter(pod) && selector.Matches(labels.Set(pod.Labels)) {