core/lib/Drupal/Core/Form/FormBuilder.php          |  1 +
 .../src/EventSubscriber/SmartCacheSubscriber.php   |  9 +------
 .../src/SmartCacheTestController.php               | 31 ++++++++++++++++++++++
 3 files changed, 33 insertions(+), 8 deletions(-)

diff --git a/core/lib/Drupal/Core/Form/FormBuilder.php b/core/lib/Drupal/Core/Form/FormBuilder.php
index cbdcaa7..b803be0 100644
--- a/core/lib/Drupal/Core/Form/FormBuilder.php
+++ b/core/lib/Drupal/Core/Form/FormBuilder.php
@@ -622,6 +622,7 @@ public function prepareForm($form_id, &$form, FormStateInterface &$form_state) {
     }
 
     // Mark every non-GET form as uncacheable.
+    // @todo Refine in https://www.drupal.org/node/2526472.
     if (!$form_state->isMethodType('get')) {
       $form['#cache']['max-age'] = 0;
     }
diff --git a/core/modules/smart_cache/src/EventSubscriber/SmartCacheSubscriber.php b/core/modules/smart_cache/src/EventSubscriber/SmartCacheSubscriber.php
index 384d889..056ea88 100644
--- a/core/modules/smart_cache/src/EventSubscriber/SmartCacheSubscriber.php
+++ b/core/modules/smart_cache/src/EventSubscriber/SmartCacheSubscriber.php
@@ -166,7 +166,7 @@ public function onRouteMatch(GetResponseEvent $event) {
   public function onResponse(FilterResponseEvent $event) {
     $response = $event->getResponse();
 
-    // SmartCache only works with HTML responses that are actual  HTMLResponse
+    // SmartCache only works with HTML responses that are actual HTMLResponse
     // objects, it does not work with plain Response objects that happen to
     // return HTML. (SmartCache needs to be able to access and modify the
     // cacheability metadata associated with the HTML response.)
@@ -207,13 +207,6 @@ public function onResponse(FilterResponseEvent $event) {
       ->addCacheContexts(['route'])
       ->addCacheTags(['rendered']);
 
-    // @todo DEBUG DEBUG DEBUG PROFILING PROFILING PROFILING — Until only the
-    //   truly uncacheable things set max-age = 0 (such as the search block and
-    //   the breadcrumbs block, which currently set max-age = 0, even though it
-    //   is perfectly possible to cache them), to see the performance boost this
-    //   will bring, uncomment this line.
-//$html_cacheability->setCacheMaxAge(Cache::PERMANENT);
-
     // SmartCache only caches cacheable HTML responses, i.e. with a max-age > 0.
     if ($html_cacheability->getCacheMaxAge() !== 0) {
       $this->normalizeCacheability($html_cacheability);
diff --git a/core/modules/smart_cache/tests/smart_cache_test/src/SmartCacheTestController.php b/core/modules/smart_cache/tests/smart_cache_test/src/SmartCacheTestController.php
index 28bb937..177d5f5 100644
--- a/core/modules/smart_cache/tests/smart_cache_test/src/SmartCacheTestController.php
+++ b/core/modules/smart_cache/tests/smart_cache_test/src/SmartCacheTestController.php
@@ -10,12 +10,27 @@
 use Drupal\Component\Utility\SafeMarkup;
 use Symfony\Component\HttpFoundation\Response;
 
+/**
+ * Controller routines for smart_cache_test routes.
+ */
 class SmartCacheTestController {
 
+  /**
+   * A route returning a Response object.
+   *
+   * @return \Symfony\Component\HttpFoundation\Response
+   *   A Response object.
+   */
   public function response() {
     return new Response('foobar');
   }
 
+  /**
+   * A route returning a render array (without cache contexts, so cacheable).
+   *
+   * @return array
+   *   A render array.
+   */
   public function html() {
     return [
       'content' => [
@@ -24,6 +39,14 @@ public function html() {
     ];
   }
 
+  /**
+   * A route returning a render array (with cache contexts, so cacheable).
+   *
+   * @return array
+   *   A render array.
+   *
+   * @see html()
+   */
   public function htmlWithCacheContexts() {
     $build = $this->html();
     $build['dynamic_part'] = [
@@ -37,6 +60,14 @@ public function htmlWithCacheContexts() {
     return $build;
   }
 
+  /**
+   * A route returning a render array (with max-age=0, so uncacheable)
+   *
+   * @return array
+   *   A render array.
+   *
+   * @see html()
+   */
   public function htmlUncacheable() {
     $build = $this->html();
     $build['very_dynamic_part'] = [