diff --git a/core/core.services.yml b/core/core.services.yml
index 59d17aa..6dd5b16 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -482,10 +482,10 @@ services:
     lazy: true
   extension.list.module:
     class: Drupal\Core\Extension\ModuleExtensionList
-    arguments: ['@app.root', 'module', '@cache.default', '@info_parser', '@module_handler', '@config.factory', '@extension.list.profile']
+    arguments: ['@app.root', 'module', '@cache.default', '@info_parser', '@module_handler', '@state', '@config.factory', '@extension.list.profile']
   extension.list.profile:
     class: Drupal\Core\Extension\ProfileExtensionList
-    arguments: ['@app.root', 'profile', '@cache.default', '@info_parser', '@module_handler']
+    arguments: ['@app.root', 'profile', '@cache.default', '@info_parser', '@module_handler', '@state']
   content_uninstall_validator:
     class: Drupal\Core\Entity\ContentUninstallValidator
     tags:
diff --git a/core/lib/Drupal/Core/Extension/ExtensionList.php b/core/lib/Drupal/Core/Extension/ExtensionList.php
index 7797cfd..05338c6 100644
--- a/core/lib/Drupal/Core/Extension/ExtensionList.php
+++ b/core/lib/Drupal/Core/Extension/ExtensionList.php
@@ -3,6 +3,7 @@
 namespace Drupal\Core\Extension;
 
 use Drupal\Core\Cache\CacheBackendInterface;
+use Drupal\Core\State\StateInterface;
 
 /**
  * Provides available extensions.
@@ -90,6 +91,13 @@
   protected $addedFileNames = [];
 
   /**
+   * The state.
+   *
+   * @var \Drupal\Core\State\StateInterface
+   */
+  protected $state;
+
+  /**
    * Constructs a new instance.
    *
    * @param string $root
@@ -102,13 +110,16 @@
    *   The info parser.
    * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
    *   The module handler.
+   * @param \Drupal\Core\State\StateInterface $state
+   *   The state.
    */
-  public function __construct($root, $type, CacheBackendInterface $cache, InfoParserInterface $info_parser, ModuleHandlerInterface $module_handler) {
+  public function __construct($root, $type, CacheBackendInterface $cache, InfoParserInterface $info_parser, ModuleHandlerInterface $module_handler, StateInterface $state) {
     $this->root = $root;
     $this->type = $type;
     $this->cache = $cache;
     $this->infoParser = $info_parser;
     $this->moduleHandler = $module_handler;
+    $this->state = $state;
   }
 
   /**
@@ -129,6 +140,7 @@ public function reset() {
     $this->extensionInfo = NULL;
     $this->cache->delete($this->getInfoCacheId());
     $this->fileNames = NULL;
+    $this->state->delete($this->getFilenameCacheId());
     $this->cache->delete($this->getFilenameCacheId());
     $this->addedFileNames = [];
     return $this;
@@ -380,8 +392,13 @@ public function getFilenames() {
       if ($cache = $this->cache->get($cache_id)) {
         $file_names = $cache->data;
       }
+      elseif ($file_names = $this->state->get($this->getFilenameCacheId())) {
+      }
       else {
         $file_names = $this->recalculateFilenames();
+        // Store filenames to allow drupal_get_filename() to retrieve them without
+        // having to rebuild or scan the filesystem.
+        $this->state->set($cache, $file_names);
         $this->cache->set($cache_id, $file_names);
       }
       $this->fileNames = $file_names;
diff --git a/core/lib/Drupal/Core/Extension/ModuleExtensionList.php b/core/lib/Drupal/Core/Extension/ModuleExtensionList.php
index 454d1f9..20c4cfa 100644
--- a/core/lib/Drupal/Core/Extension/ModuleExtensionList.php
+++ b/core/lib/Drupal/Core/Extension/ModuleExtensionList.php
@@ -4,6 +4,7 @@
 
 use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Config\ConfigFactoryInterface;
+use Drupal\Core\State\StateInterface;
 use Drupal\Core\StringTranslation\StringTranslationTrait;
 
 /**
@@ -51,13 +52,15 @@ class ModuleExtensionList extends ExtensionList {
    *   The info parser.
    * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
    *   The module handler.
+   * @param \Drupal\Core\State\StateInterface $state
+   *   The state.
    * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
    *   The config factory.
    * @param \Drupal\Core\Extension\ExtensionList $profile_list
    *   The site profile listing.
    */
-  public function __construct($root, $type, CacheBackendInterface $cache, InfoParserInterface $info_parser, ModuleHandlerInterface $module_handler, ConfigFactoryInterface $config_factory, ExtensionList $profile_list) {
-    parent::__construct($root, $type, $cache, $info_parser, $module_handler);
+  public function __construct($root, $type, CacheBackendInterface $cache, InfoParserInterface $info_parser, ModuleHandlerInterface $module_handler, StateInterface $state, ConfigFactoryInterface $config_factory, ExtensionList $profile_list) {
+    parent::__construct($root, $type, $cache, $info_parser, $module_handler, $state);
 
     $this->configFactory = $config_factory;
     $this->profileList = $profile_list;
diff --git a/core/modules/simpletest/src/KernelTestBase.php b/core/modules/simpletest/src/KernelTestBase.php
index a083805..a2e38f8 100644
--- a/core/modules/simpletest/src/KernelTestBase.php
+++ b/core/modules/simpletest/src/KernelTestBase.php
@@ -100,7 +100,7 @@ function __construct($test_id = NULL) {
   protected function beforePrepareEnvironment() {
     // Copy/prime extension file lists once to avoid filesystem scans.
     if (!isset($this->moduleFiles)) {
-      $this->moduleFiles = \Drupal::cache('default')->get('system.module.files') ?: array();
+      $this->moduleFiles = \Drupal::state()->get('system.module.files') ?: array();
       $this->themeFiles = \Drupal::state()->get('system.theme.files') ?: array();
     }
   }
diff --git a/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php b/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php
index 2c92f74..d0396a4 100644
--- a/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php
+++ b/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php
@@ -20,7 +20,7 @@ function testDrupalGetFilename() {
     global $install_state;
     $install_state['parameters']['profile'] = 'testing';
 
-    // Rebuild system.module.files state data.
+    // Rebuild the filename data.
     system_rebuild_module_data();
 
     // Retrieving the location of a module.
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index e8acdb7..b8aa83c 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -915,11 +915,13 @@ function system_check_directory($form_element, FormStateInterface $form_state) {
  */
 function system_get_info($type, $name = NULL) {
   if ($type == 'module') {
+    /** @var \Drupal\Core\Extension\ModuleExtensionList $module_list */
+    $module_list = \Drupal::service('extension.list.module');
     if (isset($name)) {
-      return \Drupal::service('extension.list.module')->getInfo($name);
+      return $module_list->getExtensionInfo($name);
     }
     else {
-      return \Drupal::service('extension.list.module')->getAllInfo();
+      return $module_list->getAllInstalledInfo();
     }
   }
   else {
diff --git a/core/tests/Drupal/Tests/Core/Extension/ExtensionListTest.php b/core/tests/Drupal/Tests/Core/Extension/ExtensionListTest.php
index a90e91c..c65dac9 100644
--- a/core/tests/Drupal/Tests/Core/Extension/ExtensionListTest.php
+++ b/core/tests/Drupal/Tests/Core/Extension/ExtensionListTest.php
@@ -9,6 +9,7 @@
 use Drupal\Core\Extension\ExtensionList;
 use Drupal\Core\Extension\InfoParserInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\State\StateInterface;
 use Drupal\Tests\UnitTestCase;
 use org\bovigo\vfs\vfsStream;
 use Prophecy\Argument;
@@ -24,8 +25,8 @@ class ExtensionListTest extends UnitTestCase {
    * @expectedException \InvalidArgumentException
    */
   public function testGetNameWithNonExistingExtension() {
-    list($cache, $info_parser, $module_handler) = $this->getMocks();
-    $test_extension_list = new TestExtension($this->root, 'test_extension', $cache->reveal(), $info_parser->reveal(), $module_handler->reveal());
+    list($cache, $info_parser, $module_handler, $state) = $this->getMocks();
+    $test_extension_list = new TestExtension($this->root, 'test_extension', $cache->reveal(), $info_parser->reveal(), $module_handler->reveal(), $state->reveal());
 
     $extension_discovery = $this->prophesize(ExtensionDiscovery::class);
     $extension_discovery->scan('test_extension')->willReturn([]);
@@ -48,8 +49,8 @@ public function testGetName() {
    * @expectedException \InvalidArgumentException
    */
   public function testGetExtensionWithNonExistingExtension() {
-    list($cache, $info_parser, $module_handler) = $this->getMocks();
-    $test_extension_list = new TestExtension($this->root, 'test_extension', $cache->reveal(), $info_parser->reveal(), $module_handler->reveal());
+    list($cache, $info_parser, $module_handler, $state) = $this->getMocks();
+    $test_extension_list = new TestExtension($this->root, 'test_extension', $cache->reveal(), $info_parser->reveal(), $module_handler->reveal(), $state->reveal());
 
     $extension_discovery = $this->prophesize(ExtensionDiscovery::class);
     $extension_discovery->scan('test_extension')->willReturn([]);
@@ -191,12 +192,12 @@ protected function setupTestExtensionList($extension_names = ['test_name']) {
       touch("vfs://drupal_root/example/$extension_name/$extension_name.info.yml", 123456789);
     }
 
-    list($cache, $info_parser, $module_handler) = $this->getMocks();
+    list($cache, $info_parser, $module_handler, $state) = $this->getMocks();
     $info_parser->parse(Argument::any())->will(function($args) {
       return Yaml::decode(file_get_contents($args[0]));
     });
 
-    $test_extension_list = new TestExtension('vfs://drupal_root', 'test_extension', $cache->reveal(), $info_parser->reveal(), $module_handler->reveal());
+    $test_extension_list = new TestExtension('vfs://drupal_root', 'test_extension', $cache->reveal(), $info_parser->reveal(), $module_handler->reveal(), $state->reveal());
 
     $extension_discovery = $this->prophesize(ExtensionDiscovery::class);
     $extension_scan_result = [];
@@ -212,7 +213,8 @@ protected function getMocks() {
     $cache = $this->prophesize(CacheBackendInterface::class);
     $info_parser = $this->prophesize(InfoParserInterface::class);
     $module_handler = $this->prophesize(ModuleHandlerInterface::class);
-    return [$cache, $info_parser, $module_handler];
+    $state = $this->prophesize(StateInterface::class);
+    return [$cache, $info_parser, $module_handler, $state];
   }
 
 }