diff --git a/core/lib/Drupal/Core/Cache/MemoryBackend.php b/core/lib/Drupal/Core/Cache/MemoryBackend.php
index 438dcdad9b..975493c683 100644
--- a/core/lib/Drupal/Core/Cache/MemoryBackend.php
+++ b/core/lib/Drupal/Core/Cache/MemoryBackend.php
@@ -64,17 +64,17 @@ public function getMultiple(&$cids, $allow_invalid = FALSE) {
    * Checks that items are either permanent or did not expire, and returns data
    * as appropriate.
    *
-   * @param object $cache
+   * @param array $cache
    *   An item loaded from self::get() or self::getMultiple().
    * @param bool $allow_invalid
    *   (optional) If TRUE, cache items may be returned even if they have expired
    *   or been invalidated.
    *
-   * @return mixed
+   * @return object|false
    *   The item with data as appropriate or FALSE if there is no
    *   valid item to load.
    */
-  protected function prepareItem($cache, $allow_invalid) {
+  protected function prepareItem(array $cache, $allow_invalid) {
     if (!isset($cache['data'])) {
       return FALSE;
     }
@@ -99,6 +99,9 @@ public function set($cid, $data, $expire = Cache::PERMANENT, array $tags = []) {
     $tags = array_unique($tags);
     // Sort the cache tags so that they are stored consistently in the database.
     sort($tags);
+
+    // Do not create an object at this point to minimise the number of objects
+    // garbage collection has to keep a track off.
     $this->cache[$cid] = [
       'cid' => $cid,
       'data' => serialize($data),
diff --git a/core/lib/Drupal/Core/Cache/MemoryCache/MemoryCache.php b/core/lib/Drupal/Core/Cache/MemoryCache/MemoryCache.php
index e546eba04f..c6fa20ba98 100644
--- a/core/lib/Drupal/Core/Cache/MemoryCache/MemoryCache.php
+++ b/core/lib/Drupal/Core/Cache/MemoryCache/MemoryCache.php
@@ -8,33 +8,21 @@
 /**
  * Defines a memory cache implementation.
  *
- * Stores cache items in memory using a PHP array.
+ * Stores cache items in memory using a PHP array. Cache data is not serialised
+ * thereby returning the same object as was cached.
  *
  * @ingroup cache
  */
 class MemoryCache extends MemoryBackend implements MemoryCacheInterface {
 
   /**
-   * Prepares a cached item.
-   *
-   * Checks that items are either permanent or did not expire, and returns data
-   * as appropriate.
-   *
-   * @param object $cache
-   *   An item loaded from self::get() or self::getMultiple().
-   * @param bool $allow_invalid
-   *   (optional) If TRUE, cache items may be returned even if they have expired
-   *   or been invalidated. Defaults to FALSE.
-   *
-   * @return mixed
-   *   The item with data as appropriate or FALSE if there is no
-   *   valid item to load.
+   * {@inheritdoc}
    */
-  protected function prepareItem($cache, $allow_invalid = FALSE) {
-    $prepared = (object) $cache;
-    if (!isset($prepared->data)) {
+  protected function prepareItem(array $cache, $allow_invalid = FALSE) {
+    if (!isset($cache['data'])) {
       return FALSE;
     }
+    $prepared = (object) $cache;
     // Check expire time.
     $prepared->valid = $prepared->expire == static::CACHE_PERMANENT || $prepared->expire >= $this->getRequestTime();
 
@@ -52,8 +40,11 @@ public function set($cid, $data, $expire = MemoryCacheInterface::CACHE_PERMANENT
     assert(Inspector::assertAllStrings($tags), 'Cache tags must be strings.');
     $tags = array_unique($tags);
 
+    // Do not create an object at this point to minimise the number of objects
+    // garbage collection has to keep a track off.
     $this->cache[$cid] = [
       'cid' => $cid,
+      // Note that $data is not serialized.
       'data' => $data,
       'created' => $this->getRequestTime(),
       'expire' => $expire,