reverted:
--- b/src/Form/IndexStatusForm.php
+++ a/src/Form/IndexStatusForm.php
@@ -65,7 +65,6 @@
     $form['#attached']['library'][] = 'search_api/drupal.search_api.admin_css';
 
     if ($index->hasValidTracker()) {
-      $tracker = $index->getTrackerInstance();
       if (!$this->getIndexTaskManager()->isTrackingComplete($index)) {
         $form['tracking'] = array(
           '#type' => 'details',
@@ -83,29 +82,6 @@
         );
       }
 
-
-      // Add the "Index details per datasource".
-      $datasource_details = array();
-      $form['datasource_details'] = array(
-        '#type' => 'details',
-        '#title' => $this->t('Index details per datasource'),
-      );
-
-      $total_per_datasource = $tracker->getTotalItemsCountPerDatasource();
-      $indexed_per_datasource = $tracker->getIndexedItemsCountPerDatasource();
-
-      foreach ($total_per_datasource as $did => $count) {
-        $datasource_details[] = $this->t('@datasource: @indexed/@total indexed', array(
-          '@datasource' => $index->getDatasource($did)->label(),
-          '@indexed' => isset($indexed_per_datasource[$did]) ? $indexed_per_datasource[$did] : 0,
-          '@total' => $count,
-        ));
-      }
-      $form['datasource_details']['indexed_per_datasource'] = array(
-        '#theme' => 'item_list',
-        '#items' => $datasource_details,
-      );
-
       // Add the "Index now" form.
       $form['index'] = array(
         '#type' => 'details',
@@ -115,7 +91,7 @@
           'class' => array('container-inline'),
         ),
       );
+      $has_remaining_items = ($index->getTrackerInstance()->getRemainingItemsCount() > 0);
-      $has_remaining_items = ($tracker->getRemainingItemsCount() > 0);
       $all_value = $this->t('all', array(), array('context' => 'items to index'));
       $limit = array(
         '#type' => 'textfield',
reverted:
--- b/src/Tracker/TrackerInterface.php
+++ a/src/Tracker/TrackerInterface.php
@@ -121,29 +121,4 @@
    */
   public function getRemainingItemsCount($datasource_id = NULL);
 
-  /**
-   * Retrieves the total number of items that are being tracked for this index
-   * per datasource.
-   *
-   * @param string|null $datasource_id
-   *   (optional) The datasource to filter the total number of indexed items by.
-   *
-   * @return array
-   *   The total number of items that are tracked for this index, or for the
-   *   given datasource on this index.
-   */
-  public function getTotalItemsCountPerDatasource($datasource_id = NULL);
-
-  /**
-   * Retrieves the number of indexed items for this index per datasource.
-   *
-   * @param string|null $datasource_id
-   *   (optional) The datasource to filter the total number of indexed items by.
-   *
-   * @return array
-   *   The number of items that have been indexed in their latest state for this
-   *   index, or for the given datasource on this index.
-   */
-  public function getIndexedItemsCountPerDatasource($datasource_id = NULL);
-
 }
only in patch2:
unchanged:
--- a/search_api.theme.inc
+++ b/search_api.theme.inc
@@ -7,10 +7,12 @@
 
 use Drupal\Component\Utility\Html;
 use Drupal\Core\Render\Element;
+use Drupal\Core\Render\Markup;
 use Drupal\Core\Url;
 use Drupal\search_api\Query\QueryInterface;
 use Drupal\search_api\SearchApiException;
 use Drupal\search_api\Utility\Utility;
+use Drupal\search_api\Tracker\TrackerPerDatasourceInterface;
 
 /**
  * Returns HTML for a fields form table.
@@ -406,6 +408,32 @@ function theme_search_api_index(array $variables) {
   $rows[] = Utility::deepCopy($row);
   $classes = [];
 
+  // Add the index details per datasource.
+  if ($tracker && ($tracker instanceof TrackerPerDatasourceInterface)) {
+    $indexed_per_datasource = $tracker->getTotalItemsCountPerDatasource();
+    $total_per_datasource = $tracker->getIndexedItemsCountPerDatasource();
+
+    // Add it if our index is multiple.
+    if ($total_per_datasource && $total_per_datasource >= 2) {
+      $datasource_details = [];
+
+      foreach ($total_per_datasource as $did => $count) {
+        $datasource_details[] = t('@datasource: @indexed/@total indexed', [
+          '@datasource' => $index->getDatasource($did)->label(),
+          '@indexed' => isset($indexed_per_datasource[$did]) ? $indexed_per_datasource[$did] : 0,
+          '@total' => $count,
+        ]);
+      }
+
+      if ($datasource_details) {
+        $label = t('Index details per datasource');
+        $message = '<small>' . implode(PHP_EOL, $datasource_details) . '</small>';
+        $info = Markup::create(nl2br($message));
+        $rows[] = Utility::deepCopy($row);
+      }
+    }
+  }
+
   // Check if a server is available.
   $classes[] = 'search-api-index-summary--server';
   if ($server) {
only in patch2:
unchanged:
--- a/src/Tracker/TrackerPluginBase.php
+++ b/src/Tracker/TrackerPluginBase.php
@@ -29,9 +29,10 @@ use Drupal\search_api\Plugin\IndexPluginBase;
  * @see \Drupal\search_api\Annotation\SearchApiTracker
  * @see \Drupal\search_api\Tracker\TrackerPluginManager
  * @see \Drupal\search_api\Tracker\TrackerInterface
+ * @see \Drupal\search_api\Tracker\TrackerPerDatasourceInterface
  * @see plugin_api
  */
-abstract class TrackerPluginBase extends IndexPluginBase implements TrackerInterface {
+abstract class TrackerPluginBase extends IndexPluginBase implements TrackerInterface, TrackerPerDatasourceInterface {
 
   // @todo Move some of the methods from
   //   \Drupal\search_api\Plugin\search_api\tracker\Basic to here?