Issue #2395143 followup by amateescu: YAML parsing is very slow, cache it with FileCache

core/lib/Drupal/Core/DrupalKernel.php

@@ -431,7 +431,7 @@ public function boot() {
       }
     }
     FileCacheFactory::setConfiguration($configuration);
-    FileCacheFactory::setPrefix(hash('sha256', Settings::get('hash_salt')));
+    FileCacheFactory::setPrefix(hash('sha256', 'FileCache' . Settings::get('hash_salt')));
 
     // Initialize the container.
     $this->initializeContainer();