attribute: preallocate map in NewAllowKeysFilter and NewDenyKeysFilter

CHANGELOG.md

@@ -17,6 +17,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - ⚠️ Update `github.com/prometheus/client_golang` to `v1.21.1`, which changes the `NameValidationScheme` to `UTF8Validation`.
   This allows metrics names to keep original delimiters (e.g. `.`), rather than replacing with underscores.
   This can be reverted by setting `github.com/prometheus/common/model.NameValidationScheme` to `LegacyValidation` in `github.com/prometheus/common/model`. (#6433)
+- Initialize map with `len(keys)` in `NewAllowKeysFilter` and `NewDenyKeysFilter` to avoid unnecessary allocations in `go.opentelemetry.io/otel/attribute`. (#6455)
 
 ### Fixes
 

attribute/filter.go

@@ -19,7 +19,7 @@ func NewAllowKeysFilter(keys ...Key) Filter {
 		return func(kv KeyValue) bool { return false }
 	}
 
-	allowed := make(map[Key]struct{})
+	allowed := make(map[Key]struct{}, len(keys))
 	for _, k := range keys {
 		allowed[k] = struct{}{}
 	}
@@ -38,7 +38,7 @@ func NewDenyKeysFilter(keys ...Key) Filter {
 		return func(kv KeyValue) bool { return true }
 	}
 
-	forbid := make(map[Key]struct{})
+	forbid := make(map[Key]struct{}, len(keys))
 	for _, k := range keys {
 		forbid[k] = struct{}{}
 	}