From 3adc870f6a4ca5dc0b1a21046502383f9222b0ac Mon Sep 17 00:00:00 2001
From: John Howard <howardjohn@google.com>
Date: Wed, 21 Sep 2022 11:54:37 -0700
Subject: [PATCH 1/2] Optimize `Everything` and `Nothing` label selectors

Currently each call makes 1 small alloc. This is not much, but it adds
up when this is called millions of times. This simple change just moves
to using a shared struct between everything.

This is safe as each operation on the Selector is not doing mutations.

Kubernetes-commit: ca414d707a6b10c41b65ed9bee127773f2bcf0fc
---
 pkg/labels/selector.go | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/pkg/labels/selector.go b/pkg/labels/selector.go
index 6d6f562ad..06b0aa537 100644
--- a/pkg/labels/selector.go
+++ b/pkg/labels/selector.go
@@ -74,9 +74,11 @@ type Selector interface {
 	RequiresExactMatch(label string) (value string, found bool)
 }
 
+var everythingSelector Selector = internalSelector{}
+
 // Everything returns a selector that matches all labels.
 func Everything() Selector {
-	return internalSelector{}
+	return everythingSelector
 }
 
 type nothingSelector struct{}
@@ -91,9 +93,11 @@ func (n nothingSelector) RequiresExactMatch(label string) (value string, found b
 	return "", false
 }
 
+var internalNothingSelector Selector = nothingSelector{}
+
 // Nothing returns a selector that matches no labels
 func Nothing() Selector {
-	return nothingSelector{}
+	return internalNothingSelector
 }
 
 // NewSelector returns a nil selector

From 88a14484aadcd0bcc9dde348b53d5d679105c4ef Mon Sep 17 00:00:00 2001
From: John Howard <howardjohn@google.com>
Date: Tue, 1 Nov 2022 13:36:26 -0700
Subject: [PATCH 2/2] Rename and comment on why sharing is safe

Kubernetes-commit: 916fe2f89610a058603c1aa5260cd45841aadb0c
---
 pkg/labels/selector.go | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/pkg/labels/selector.go b/pkg/labels/selector.go
index 06b0aa537..891004389 100644
--- a/pkg/labels/selector.go
+++ b/pkg/labels/selector.go
@@ -74,11 +74,12 @@ type Selector interface {
 	RequiresExactMatch(label string) (value string, found bool)
 }
 
-var everythingSelector Selector = internalSelector{}
+// Sharing this saves 1 alloc per use; this is safe because it's immutable.
+var sharedEverythingSelector Selector = internalSelector{}
 
 // Everything returns a selector that matches all labels.
 func Everything() Selector {
-	return everythingSelector
+	return sharedEverythingSelector
 }
 
 type nothingSelector struct{}
@@ -93,11 +94,12 @@ func (n nothingSelector) RequiresExactMatch(label string) (value string, found b
 	return "", false
 }
 
-var internalNothingSelector Selector = nothingSelector{}
+// Sharing this saves 1 alloc per use; this is safe because it's immutable.
+var sharedNothingSelector Selector = nothingSelector{}
 
 // Nothing returns a selector that matches no labels
 func Nothing() Selector {
-	return internalNothingSelector
+	return sharedNothingSelector
 }
 
 // NewSelector returns a nil selector