cache the serializers for a class

lib/active_model/serializer.rb

@@ -201,7 +201,12 @@ module ActiveModel
 
     private
 
+    def self.serializers_cache
+      @serializers_cache ||= Threadsafe::Cache.new
+    end
+
     def self.get_serializer_for(klass)
+      serializers_cache.fetch_or_store(klass) do
         serializer_class_name = "#{klass.name}Serializer"
         serializer_class = serializer_class_name.safe_constantize
 
@@ -211,6 +216,7 @@ module ActiveModel
           get_serializer_for(klass.superclass)
         end
       end
+    end
 
   end
 end