Issue #2239369 by sun: "Comments per page" setting cannot be configured to be larger than 300.

core/modules/comment/comment.module

@@ -1452,14 +1452,6 @@ function template_preprocess_comment_wrapper(&$variables) {
   $variables['form'] = $variables['content']['comment_form'];
 }
 
-/**
- * Returns an array of "comments per page" values that users can select from.
- */
-function _comment_per_page() {
-  $comments_per_page = array(10, 30, 50, 70, 90, 150, 200, 250, 300);
-  return array_combine($comments_per_page, $comments_per_page);
-}
-
 /**
  * Implements hook_ranking().
  */

core/modules/comment/lib/Drupal/comment/Plugin/Field/FieldType/CommentItem.php

@@ -126,10 +126,13 @@ public function instanceSettingsForm(array $form, array &$form_state) {
       '#description' => t('Show comment replies in a threaded list.'),
     );
     $element['comment']['per_page'] = array(
-      '#type' => 'select',
+      '#type' => 'number',
       '#title' => t('Comments per page'),
       '#default_value' => $settings['per_page'],
-      '#options' => _comment_per_page(),
+      '#required' => TRUE,
+      '#min' => 10,
+      '#max' => 1000,
+      '#step' => 10,
     );
     $element['comment']['anonymous'] = array(
       '#type' => 'select',