diff --git a/core/core.services.yml b/core/core.services.yml
index e6395ee..913db85 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -85,10 +85,6 @@ services:
   cache_tag:
     class: Drupal\Core\Cache\DatabaseTagBackend
     arguments: ['@database']
-  config.cachedstorage.storage:
-    class: Drupal\Core\Config\FileStorage
-    factory_class: Drupal\Core\Config\FileStorageFactory
-    factory_method: getActive
   config.manager:
     class: Drupal\Core\Config\ConfigManager
     arguments: ['@entity.manager', '@config.factory', '@config.typed', '@string_translation', '@config.storage', '@event_dispatcher']
diff --git a/core/lib/Drupal/Core/Cache/ApcuBackend.php b/core/lib/Drupal/Core/Cache/ApcuBackend.php
index ffaeba3..f9111bd 100644
--- a/core/lib/Drupal/Core/Cache/ApcuBackend.php
+++ b/core/lib/Drupal/Core/Cache/ApcuBackend.php
@@ -36,44 +36,27 @@ class ApcuBackend implements CacheBackendInterface {
   protected $binPrefix;
 
   /**
-   * Prefix for keys holding invalidation cache tags.
+   * The cache tag factory service.
    *
-   * Includes the site-specific prefix in $sitePrefix.
-   *
-   * @var string
-   */
-  protected $invalidationsTagsPrefix;
-
-  /**
-   * Prefix for keys holding invalidation cache tags.
-   *
-   * Includes the site-specific prefix in $sitePrefix.
-   *
-   * @var string
-   */
-  protected $deletionsTagsPrefix;
-
-  /**
-   * A static cache of all tags checked during the request.
-   *
-   * @var array
+   * @var \Drupal\Core\Cache\CacheTagBackendInterface
    */
-  protected static $tagCache = array('deletions' => array(), 'invalidations' => array());
+  protected $cacheTag;
 
   /**
    * Constructs a new ApcuBackend instance.
    *
+   * @param \Drupal\Core\Cache\CacheTagBackendInterface $cache_tag
+   *   The cache tag service.
    * @param string $bin
    *   The name of the cache bin.
    * @param string $site_prefix
    *   The prefix to use for all keys in the storage that belong to this site.
    */
-  public function __construct($bin, $site_prefix) {
+  public function __construct(CacheTagBackendInterface $cache_tag, $bin, $site_prefix) {
+    $this->cacheTag = $cache_tag;
     $this->bin = $bin;
     $this->sitePrefix = $site_prefix;
     $this->binPrefix = $this->sitePrefix . '::' . $this->bin . '::';
-    $this->invalidationsTagsPrefix = $this->sitePrefix . '::itags::';
-    $this->deletionsTagsPrefix = $this->sitePrefix . '::dtags::';
   }
 
   /**
@@ -161,19 +144,18 @@ protected function prepareItem($cache, $allow_invalid) {
     }
 
     $cache->tags = $cache->tags ? explode(' ', $cache->tags) : array();
-    $checksum = $this->checksumTags($cache->tags);
-
-    // Check if deleteTags() has been called with any of the entry's tags.
-    if ($cache->checksum_deletions != $checksum['deletions']) {
-      return FALSE;
-    }
+    $this->cacheTag->prepareGet($cache);
 
     // Check expire time.
-    $cache->valid = $cache->expire == Cache::PERMANENT || $cache->expire >= REQUEST_TIME;
+    $cache->valid = $time_valid = $cache->expire == Cache::PERMANENT || $cache->expire >= REQUEST_TIME;
 
-    // Check if invalidateTags() has been called with any of the entry's tags.
-    if ($cache->checksum_invalidations != $checksum['invalidations']) {
-      $cache->valid = FALSE;
+    if ($cache->deleted) {
+      $this->delete($cache->cid);
+      return FALSE;
+    }
+
+    if ($time_valid && !$cache->valid) {
+      $this->invalidate($cache->cid);
     }
 
     if (!$allow_invalid && !$cache->valid) {
@@ -191,8 +173,8 @@ public function set($cid, $data, $expire = CacheBackendInterface::CACHE_PERMANEN
     $cache->cid = $cid;
     $cache->created = round(microtime(TRUE), 3);
     $cache->expire = $expire;
-    $cache->tags = implode(' ', $this->flattenTags($tags));
-    $checksum = $this->checksumTags($tags);
+    $cache->tags = implode(' ', $this->cacheTag->flattenTags($tags));
+    $checksum = $this->cacheTag->checksumTags($tags, TRUE);
     $cache->checksum_invalidations = $checksum['invalidations'];
     $cache->checksum_deletions = $checksum['deletions'];
     // APC serializes/unserializes any structure itself.
@@ -256,13 +238,6 @@ public function removeBin() {
   /**
    * {@inheritdoc}
    */
-  public function isEmpty() {
-    return $this->getAll()->getTotalCount() === 0;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
   public function invalidate($cid) {
     $this->invalidateMultiple(array($cid));
   }
@@ -286,91 +261,4 @@ public function invalidateAll() {
     }
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  public function deleteTags(array $tags) {
-    foreach ($this->flattenTags($tags) as $tag) {
-      apc_inc($this->deletionsTagsPrefix . $tag, 1, $success);
-      if (!$success) {
-        apc_store($this->deletionsTagsPrefix . $tag, 1);
-      }
-    }
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function invalidateTags(array $tags) {
-    foreach ($this->flattenTags($tags) as $tag) {
-      apc_inc($this->invalidationsTagsPrefix . $tag, 1, $success);
-      if (!$success) {
-        apc_store($this->invalidationsTagsPrefix . $tag, 1);
-      }
-    }
-  }
-
-  /**
-   * Flattens a tags array into a numeric array suitable for string storage.
-   *
-   * @param array $tags
-   *   Associative array of tags to flatten.
-   *
-   * @return array
-   *   Indexed array of flattened tag identifiers.
-   */
-  protected function flattenTags(array $tags) {
-    if (isset($tags[0])) {
-      return $tags;
-    }
-
-    $flat_tags = array();
-    foreach ($tags as $namespace => $values) {
-      if (is_array($values)) {
-        foreach ($values as $value) {
-          $flat_tags[] = "$namespace:$value";
-        }
-      }
-      else {
-        $flat_tags[] = "$namespace:$values";
-      }
-    }
-    return $flat_tags;
-  }
-
-  /**
-   * Returns the sum total of validations for a given set of tags.
-   *
-   * @param array $tags
-   *   Associative array of tags.
-   *
-   * @return int
-   *   Sum of all invalidations.
-   */
-  protected function checksumTags(array $tags) {
-    $checksum = array('invalidations' => 0, 'deletions' => 0);
-    $query_tags = array('invalidations' => array(), 'deletions' => array());
-
-    foreach ($this->flattenTags($tags) as $tag) {
-      foreach (array('deletions', 'invalidations') as $type) {
-        if (isset(static::$tagCache[$type][$tag])) {
-          $checksum[$type] += static::$tagCache[$type][$tag];
-        }
-        else {
-          $query_tags[$type][] = $this->{$type . 'TagsPrefix'} . $tag;
-        }
-      }
-    }
-
-    foreach (array('deletions', 'invalidations') as $type) {
-      if ($query_tags[$type]) {
-        $result = apc_fetch($query_tags[$type]);
-        static::$tagCache[$type] = array_merge(static::$tagCache[$type], $result);
-        $checksum[$type] += array_sum($result);
-      }
-    }
-
-    return $checksum;
-  }
-
 }
diff --git a/core/lib/Drupal/Core/Cache/ApcuBackendFactory.php b/core/lib/Drupal/Core/Cache/ApcuBackendFactory.php
index 341203c..0718848 100644
--- a/core/lib/Drupal/Core/Cache/ApcuBackendFactory.php
+++ b/core/lib/Drupal/Core/Cache/ApcuBackendFactory.php
@@ -19,9 +19,20 @@ class ApcuBackendFactory implements CacheFactoryInterface {
   protected $sitePrefix;
 
   /**
+   * The cache tag factory service.
+   *
+   * @var \Drupal\Core\Cache\CacheTagBackendInterface
+   */
+  protected $cacheTagBackend;
+
+  /**
    * Constructs an ApcuBackendFactory object.
+   *
+   * @param \Drupal\Core\Cache\CacheTagBackendInterface $cache_tag_backend
+   *   The cache tag service.
    */
-  public function __construct() {
+  function __construct(CacheTagBackendInterface $cache_tag_backend) {
+    $this->cacheTagBackend = $cache_tag_backend;
     $this->sitePrefix = Crypt::hashBase64(DRUPAL_ROOT . '/' . conf_path());
   }
 
@@ -35,7 +46,7 @@ public function __construct() {
    *   The cache backend object for the specified cache bin.
    */
   public function get($bin) {
-    return new ApcuBackend($bin, $this->sitePrefix);
+    return new ApcuBackend($this->cacheTagBackend, $bin, $this->sitePrefix);
   }
 
 }
diff --git a/core/lib/Drupal/Core/Cache/CacheTagBackendInterface.php b/core/lib/Drupal/Core/Cache/CacheTagBackendInterface.php
index ca31af1..6323e3b 100644
--- a/core/lib/Drupal/Core/Cache/CacheTagBackendInterface.php
+++ b/core/lib/Drupal/Core/Cache/CacheTagBackendInterface.php
@@ -65,7 +65,7 @@ public function checksumTags(array $tags, $set_context);
    * $item->deleted should be set to TRUE if item was deleted via tags and
    * $item->valid should be set to FALSE if item was invalidated.
    */
-  public function prepareGet(&$item);
+  public function prepareGet($item);
 
   /**
    * Clears cache tag service internal caches.
diff --git a/core/lib/Drupal/Core/Cache/DatabaseTagBackend.php b/core/lib/Drupal/Core/Cache/DatabaseTagBackend.php
index 8fd66c9..526dd01 100644
--- a/core/lib/Drupal/Core/Cache/DatabaseTagBackend.php
+++ b/core/lib/Drupal/Core/Cache/DatabaseTagBackend.php
@@ -173,7 +173,7 @@ public function checksumTags(array $tags, $set_context) {
   /**
    * {@inheritdoc}
    */
-  public function prepareGet(&$item) {
+  public function prepareGet($item) {
     $checksum = $this->checksumTags($item->tags, FALSE);
 
     // Check if deleteTags() has been called with any of the entry's tags.
diff --git a/core/lib/Drupal/Core/Cache/MemoryBackendFactory.php b/core/lib/Drupal/Core/Cache/MemoryBackendFactory.php
index 093b373..75ddb36 100644
--- a/core/lib/Drupal/Core/Cache/MemoryBackendFactory.php
+++ b/core/lib/Drupal/Core/Cache/MemoryBackendFactory.php
@@ -10,16 +10,17 @@
 class MemoryBackendFactory implements CacheFactoryInterface {
 
   /**
-   * The cache tag factory service.
+   * The cache tag service.
    *
    * @var \Drupal\Core\Cache\CacheTagBackendInterface
    */
   protected $cacheTagBackend;
 
   /**
-   * Constructs the DatabaseBackendFactory object.
+   * Constructs the MemoryBackendFactory object.
    *
-   * @param \Drupal\Core\Database\Connection $connection
+   * @param \Drupal\Core\Cache\CacheTagBackendInterface $cache_tag_backend
+   *   The cache tag service.
    */
   function __construct(CacheTagBackendInterface $cache_tag_backend) {
     $this->cacheTagBackend = $cache_tag_backend;
diff --git a/core/lib/Drupal/Core/Cache/MemoryTagBackend.php b/core/lib/Drupal/Core/Cache/MemoryTagBackend.php
index 4920b05..9bbc8cb 100644
--- a/core/lib/Drupal/Core/Cache/MemoryTagBackend.php
+++ b/core/lib/Drupal/Core/Cache/MemoryTagBackend.php
@@ -8,9 +8,10 @@
 namespace Drupal\Core\Cache;
 
 /**
- * Class MemoryTagBackend.
+ * Memory cache tags implementation.
  */
 class MemoryTagBackend extends CacheTagBackendBase {
+
   /**
    * The cache tag storage.
    *
@@ -74,7 +75,7 @@ public function checksumTags(array $tags, $set_context) {
   /**
    * {@inheritdoc}
    */
-  public function prepareGet(&$item) {
+  public function prepareGet($item) {
     $checksum = $this->checksumTags($item->tags, FALSE);
 
     // Check if deleteTags() has been called with any of the entry's tags.
diff --git a/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
index 1b457d7..988bfa9 100644
--- a/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -868,7 +868,6 @@ protected function setUp() {
     // Execute the non-interactive installer.
     require_once DRUPAL_ROOT . '/core/includes/install.core.inc';
     $this->settingsSet('cache', array('default' => 'cache.backend.memory'));
-    $this->settingsSet('cache_tag_service', 'cache.tag.memory');
     $parameters = $this->installParameters();
 
     install_drupal($parameters);
@@ -1172,7 +1171,7 @@ protected function resetAll() {
    */
   protected function refreshVariables() {
     // Clear the tag cache.
-    $this->container->get('cache.tag')->clearCache();
+    $this->container->get('cache_tag')->clearCache();
 
     $this->container->get('config.factory')->reset();
     $this->container->get('state')->resetCache();
diff --git a/core/tests/Drupal/Tests/UnitTestCase.php b/core/tests/Drupal/Tests/UnitTestCase.php
index 1dc8b0b..65000a1 100644
--- a/core/tests/Drupal/Tests/UnitTestCase.php
+++ b/core/tests/Drupal/Tests/UnitTestCase.php
@@ -217,8 +217,7 @@ public function getStringTranslationStub() {
    */
   protected function getContainerWithCacheTags(CacheTagBackendInterface $backend) {
     $container = new ContainerBuilder();
-    $container->setParameter('cache_tags', array('cache.tag.test' => 'test'));
-    $container->set('cache.tag.test', $backend);
+    $container->set('cache_tag', $backend);
 
     \Drupal::setContainer($container);
     return $container;