Issue #2800605 by Chi, Wim Leers, dhirendra.mishra, mr.baileys, jheds…

…trom, dawehner, borisson_, catch, alexpott: Warn/inform users when the hosting environment has a too low limit of APCU cache

(cherry picked from commit cee0a334817b123ae57127a1d37d8e721542e8da)

modules/system/system.install

@@ -6,6 +6,7 @@
  */
 
 use Drupal\Component\FileSystem\FileSystem as FileSystemComponent;
+use Drupal\Component\Utility\Bytes;
 use Drupal\Component\Utility\Crypt;
 use Drupal\Component\Utility\Environment;
 use Drupal\Component\Utility\OpCodeCache;
@@ -311,6 +312,46 @@ function system_requirements($phase) {
     $requirements['php_opcache']['title'] = t('PHP OPcode caching');
   }
 
+  // Check to see if APCu is installed and configured correctly.
+  if ($phase == 'runtime' && PHP_SAPI != 'cli') {
+    $requirements['php_apcu']['title'] = t('PHP APCu caching');
+    if (extension_loaded('apcu') && filter_var(ini_get('apc.enabled'), FILTER_VALIDATE_BOOLEAN)) {
+      $memory_info = apcu_sma_info(TRUE);
+      $apcu_actual_size = format_size($memory_info['seg_size']);
+      $apcu_recommended_size = '32 MB';
+      $requirements['php_apcu']['value'] = t('Enabled (@size)', ['@size' => $apcu_actual_size]);
+      if (Bytes::toInt($apcu_actual_size) < Bytes::toInt($apcu_recommended_size)) {
+        $requirements['php_apcu']['severity'] = REQUIREMENT_WARNING;
+        $requirements['php_apcu']['description'] = t('Depending on your configuration, Drupal can run with a @apcu_size APCu limit. However, a @apcu_default_size APCu limit (the default) or above is recommended, especially if your site uses additional custom or contributed modules.', [
+          '@apcu_size' => $apcu_actual_size,
+          '@apcu_default_size' => $apcu_recommended_size,
+        ]);
+      }
+      else {
+        $memory_available = $memory_info['avail_mem'] / $memory_info['seg_size'];
+        if ($memory_available < 0.1) {
+          $requirements['php_apcu']['severity'] = REQUIREMENT_ERROR;
+        }
+        elseif ($memory_available < 0.25) {
+          $requirements['php_apcu']['severity'] = REQUIREMENT_WARNING;
+        }
+        else {
+          $requirements['php_apcu']['severity'] = REQUIREMENT_OK;
+        }
+        $requirements['php_apcu']['description'] = t('Memory available: @available.', [
+          '@available' => format_size($memory_info['avail_mem']),
+        ]);
+      }
+    }
+    else {
+      $requirements['php_apcu'] += [
+        'value' => t('Not enabled'),
+        'severity' => REQUIREMENT_INFO,
+        'description' => t('PHP APCu caching can improve your site\'s performance considerably. It is <strong>highly recommended</strong> to have <a href="https://www.php.net/manual/apcu.installation.php" target="_blank">APCu</a> installed on your server.'),
+      ];
+    }
+  }
+
   if ($phase != 'update') {
     // Test whether we have a good source of random bytes.
     $requirements['php_random_bytes'] = [