diff --git a/core/modules/migrate/src/EventSubscriber/MemoryLimitExceeded.php b/core/modules/migrate/src/EventSubscriber/MemoryLimitExceeded.php
index 9ce3fdccad..682b462e07 100644
--- a/core/modules/migrate/src/EventSubscriber/MemoryLimitExceeded.php
+++ b/core/modules/migrate/src/EventSubscriber/MemoryLimitExceeded.php
@@ -97,42 +97,26 @@ public function reclaim(MigrateMemoryLimitEvent $event) {
    *   A migrate memory limit event.
    */
   public function notify(MigrateMemoryLimitEvent $event) {
-    $percent = round($event->getUsageRatio() * 100);
-    $usage = format_size($event->getUsageInBytes());
-    $limit = format_size($event->getLimit());
+    $results = [
+      '@pct' => round($event->getUsageRatio() * 100),
+      '@usage' => format_size($event->getUsageInBytes()),
+      '@limit' => format_size($event->getLimit()),
+    ];
     switch ($event->getPhase()) {
       case MemoryManagerInterface::PRE_RECLAIMED:
         $this->message->display($this->t(
-          'Memory usage is @usage (@pct% of limit @limit), reclaiming memory.',
-          [
-            '@pct' => $percent,
-            '@usage' => $usage,
-            '@limit' => $limit,
-          ]
-        ), 'warning');
+          'Memory usage is @usage (@pct% of limit @limit), reclaiming memory.', $results), 'warning');
         break;
 
       case MemoryManagerInterface::STILL_EXCEEDED:
         $this->message->display($this->t(
-          'Memory usage is now @usage (@pct% of limit @limit), not enough reclaimed, starting new batch',
-          [
-            '@pct' => $percent,
-            '@usage' => $usage,
-            '@limit' => $limit,
-          ]
-        ), 'warning');
+          'Memory usage is now @usage (@pct% of limit @limit), not enough reclaimed, starting new batch', $results), 'warning');
         break;
 
       case MemoryManagerInterface::REDUCED_ENOUGH_TO_CONTINUE:
       case '':
         $this->message->display($this->t(
-          'Memory usage is now @usage (@pct% of limit @limit), reclaimed enough, continuing',
-          [
-            '@pct' => $percent,
-            '@usage' => $usage,
-            '@limit' => $limit,
-          ]
-        ));
+          'Memory usage is now @usage (@pct% of limit @limit), reclaimed enough, continuing', $results));
         break;
     }
   }
diff --git a/core/modules/migrate/src/MemoryManagerInterface.php b/core/modules/migrate/src/MemoryManagerInterface.php
index 55b3e11f7a..a799159fd1 100644
--- a/core/modules/migrate/src/MemoryManagerInterface.php
+++ b/core/modules/migrate/src/MemoryManagerInterface.php
@@ -25,11 +25,14 @@ interface MemoryManagerInterface {
   /**
    * Tests whether we've exceeded the desired memory threshold.
    *
+   * If memory usage is too high, then dispatch a PRE_RECLAIMED MigrateEvent so
+   * that event listeners can reclaim memory. Then dispatch a STILL_EXCEEDED
+   * MigrateEvent or a REDUCED_ENOUGH_TO_CONTINUE MigrateEvent, depending on
+   * whether enough memory was reclaimed.
+   *
    * @return bool
-   *   TRUE if the threshold is exceeded, otherwise FALSE. If memory usage has
-   *   exceeded the limit then a PRE_RECLAIMED MigrateEvent is dispatched, This
-   *   is followed by either a STILL_EXCEEDED MigrateEvent or a
-   *   REDUCED_ENOUGH_TO_CONTINUE MigrateEvent if enough memory was reclaimed.
+   * TRUE if memory usage is low enough, or if enough memory can be reclaimed.
+   * FALSE if memory usage is too high and not enough can be reclaimed.
    */
   public function ensureMemory();
 
diff --git a/core/modules/migrate/src/MigrateExecutable.php b/core/modules/migrate/src/MigrateExecutable.php
index d14a9bcd7c..c218ea6b38 100644
--- a/core/modules/migrate/src/MigrateExecutable.php
+++ b/core/modules/migrate/src/MigrateExecutable.php
@@ -133,7 +133,7 @@ protected function getEventDispatcher() {
   /**
    * Gets the migration memory manager.
    *
-   * @return \Drupal\migrate\MemoryManager
+   * @return \Drupal\migrate\MemoryManagerInterface
    *   The migration memory manager.
    */
   protected function getMemoryManager() {