Release the entire env

config.ru

@@ -23,6 +23,6 @@ warmup do |app|
 end
 
 map ENV['RAILS_RELATIVE_URL_ROOT'] || "/" do
-  use Gitlab::ReleaseController
+  use Gitlab::Middleware::ReleaseEnv
   run Gitlab::Application
 end

lib/gitlab/middleware/release_controller.rb

@@ -1,9 +0,0 @@
-module Gitlab
-  module Middleware
-    ReleaseController = Struct.new(:app) do
-      def call(env)
-        app.call(env).tap { env.delete('action_controller.instance') }
-      end
-    end
-  end
-end

lib/gitlab/middleware/release_env.rb

@@ -0,0 +1,14 @@
+module Gitlab
+  module Middleware
+    # Some of middleware would hold env for no good reason even after the
+    # request had already been processed, and we could not garbage collect
+    # them due to this. Put this middleware as the first middleware so that
+    # it would clear the env after the request is done, allowing GC gets a
+    # chance to release memory for the last request.
+    ReleaseEnv = Struct.new(:app) do
+      def call(env)
+        app.call(env).tap { env.clear }
+      end
+    end
+  end
+end

spec/lib/gitlab/middleware/release_env_spec.rb

@@ -1,6 +1,6 @@
 require 'spec_helper'
 
-describe Gitlab::Middleware::ReleaseController do
+describe Gitlab::Middleware::ReleaseEnv do
   let(:inner_app) { double(:app) }
   let(:app) { described_class.new(inner_app) }
   let(:env) { { 'action_controller.instance' => 'something' } }