Demonstrate the memory leak in ruby-grape#2102 with remounting.

Gemfile

@@ -17,6 +17,7 @@ end
 group :development do
   gem 'appraisal'
   gem 'benchmark-ips'
+  gem 'benchmark-memory'
   gem 'guard'
   gem 'guard-rspec'
   gem 'guard-rubocop'

benchmark/remounting.rb

@@ -0,0 +1,47 @@
+$LOAD_PATH.unshift(File.join(File.dirname(__FILE__), '..', 'lib'))
+require 'grape'
+require 'benchmark/memory'
+
+class VotingApi < Grape::API
+  logger Logger.new(STDOUT)
+
+  helpers do
+    def logger
+      VotingApi.logger
+    end
+  end
+
+  namespace 'votes' do
+    get do
+      logger
+    end
+  end
+end
+
+class PostApi < Grape::API
+  mount VotingApi
+end
+
+class CommentAPI < Grape::API
+  mount VotingApi
+end
+
+env = Rack::MockRequest.env_for('/votes', method: 'GET')
+
+Benchmark.memory do |api|
+  calls = 1000
+
+  api.report('using Array') do
+    VotingApi.instance_variable_set(:@setup, [])
+    calls.times { PostApi.call(env) }
+    puts " setup size: #{VotingApi.instance_variable_get(:@setup).size}"
+  end
+
+  api.report('using Set') do
+    VotingApi.instance_variable_set(:@setup, Set.new)
+    calls.times { PostApi.call(env) }
+    puts " setup size: #{VotingApi.instance_variable_get(:@setup).size}"
+  end
+
+  api.compare!
+end