preallocate memory

[florianl]

What this PR does / why we need it:

Preallocate memory instead of enforcing an incremental growth. This will result in less work for the garbage collector.

[k8s-ci-robot]

@florianl: This PR has multiple commits, and the default merge method is: merge.
You can request commits to be squashed using the label: tide/merge-method-squash

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: florianl / name: Florian Lehner (0fbaa2d, c2312c4)

[k8s-ci-robot]

Welcome @florianl!

It looks like this is your first PR to kubernetes-sigs/kustomize 🎉. Please refer to our pull request process documentation to help your PR have a smooth ride to approval.

You will be prompted by a bot to use commands during the review process. Do not be afraid to follow the prompts! It is okay to experiment. Here is the bot commands documentation.

You can also check if kubernetes-sigs/kustomize has its own contribution guidelines.

You may want to refer to our testing guide if you run into trouble with your tests not passing.

If you are having difficulty getting your pull request seen, please follow the recommended escalation practices. Also, for tips and tricks in the contribution process you may want to read the Kubernetes contributor cheat sheet. We want to make sure your contribution gets all the attention it needs!

Thank you, and welcome to Kubernetes. 😃

[k8s-ci-robot]

Hi @florianl. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[florianl]

friendly ping at @mengqiy and @mortent - do you have feedback for me on this PR?

[natasha41575]

If this results in a performance improvement, could you please provide some example test cases that demonstrate the optimization? You can refer to #4810 as an example, the PR description does a good job of explaining the optimization.

[florianl]

hi @natasha41575

I'm not sure if it is worth including a benchmark in this PR. But to showcase the performance improvement, I did use the following code:

func BenchmarkStringList(b *testing.B) {
	s := make(String)
	// Prepare s
	for i := 0; i < 1000; i++ {
		s.Insert(fmt.Sprintf("%d", i))
	}
	// Run the benchmark
	for i := 0; i < b.N; i++ {
		list := s.List()
		_ = list
	}
}

On my machine the results for BenchmarkStringList() on this branch are:

$ go test -bench=. -benchmem
goos: linux
goarch: amd64
pkg: sigs.k8s.io/kustomize/kyaml/sets
cpu: AMD Ryzen 7 PRO 4750U with Radeon Graphics
BenchmarkStringList-16    	   34600	     35118 ns/op	   16389 B/op	       1 allocs/op
PASS
ok  	sigs.k8s.io/kustomize/kyaml/sets	1.574s

To compare it with the results from master:

$ go test -bench=. -benchmem
goos: linux
goarch: amd64
pkg: sigs.k8s.io/kustomize/kyaml/sets
cpu: AMD Ryzen 7 PRO 4750U with Radeon Graphics
BenchmarkStringList-16    	   24054	     54318 ns/op	   50423 B/op	      12 allocs/op
PASS
ok  	sigs.k8s.io/kustomize/kyaml/sets	1.816s

So this trivial change reduces the ns/op (from 54318 to 35118) and allocs/op (from 12 to 1).

[natasha41575]

Thanks!
/ok-to-test

[natasha41575]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: florianl, natasha41575

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• kyaml/OWNERS [natasha41575]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment