[DI] Document the container preload tags

Author: javiereguiluz

performance.rst

@@ -122,6 +122,10 @@ The preload file path is the same as the compiled service container but with the
     ; php.ini
     opcache.preload=/path/to/project/var/cache/prod/srcApp_KernelProdContainer.preload.php
 
+Use the :ref:`container.preload <dic-tags-container-preload>` and
+:ref:`container.no_preload <dic-tags-container-nopreload>` service tags to define
+which classes should or should not be preloaded PHP.
+
 .. _performance-configure-opcache:
 
 Configure OPcache for Maximum Performance

reference/dic_tags.rst

@@ -14,6 +14,8 @@ Tag Name                                  Usage
 `auto_alias`_                             Define aliases based on the value of container parameters
 `console.command`_                        Add a command
 `container.hot_path`_                     Add to list of always needed services
+`container.no_preload`_                   Remove a class from the list of classes preloaded by PHP
+`container.preload`_                      Add some class to the list of classes preloaded by PHP
 `controller.argument_value_resolver`_     Register a value resolver for controller arguments such as ``Request``
 `data_collector`_                         Create a class that collects custom data for the profiler
 `doctrine.event_listener`_                Add a Doctrine event listener
@@ -212,6 +214,109 @@ for services and their class hierarchy. The result is as significant performance
 
 Use this tag with great caution, you have to be sure that the tagged service is always used.
 
+.. _dic-tags-container-nopreload:
+
+container.no_preload
+--------------------
+
+**Purpose**: Remove a class from the list of classes preloaded by PHP
+
+.. versionadded:: 5.1
+
+    The ``container.no_preload`` tag was introduced in Symfony 5.1.
+
+Add this tag to a service and its class won't be preloaded when using
+`PHP class preloading`_:
+
+.. configuration-block::
+
+    .. code-block:: yaml
+
+        services:
+            App\SomeNamespace\SomeService:
+                tags: ['container.no_preload']
+
+    .. code-block:: xml
+
+        <?xml version="1.0" encoding="UTF-8" ?>
+        <container xmlns="http://symfony.com/schema/dic/services"
+            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+            xsi:schemaLocation="http://symfony.com/schema/dic/services
+                https://symfony.com/schema/dic/services/services-1.0.xsd">
+
+            <services>
+                <service id="App\SomeNamespace\SomeService">
+                    <tag name="container.no_preload"/>
+                </service>
+            </services>
+        </container>
+
+    .. code-block:: php
+
+        use App\SomeNamespace\SomeService;
+
+        $container
+            ->register(SomeService::class)
+            ->addTag('container.no_preload')
+        ;
+
+.. _dic-tags-container-preload:
+
+container.preload
+-----------------
+
+**Purpose**: Add some class to the list of classes preloaded by PHP
+
+.. versionadded:: 5.1
+
+    The ``container.preload`` tag was introduced in Symfony 5.1.
+
+When using `PHP class preloading`_, this tag allows you to define which PHP
+classes should be preloaded. This can improve performance by making some of the
+classes used by your service always available for all requests (until the server
+is restarted):
+
+.. configuration-block::
+
+    .. code-block:: yaml
+
+        services:
+            App\SomeNamespace\SomeService:
+                tags:
+                    - { name: 'container.preload', class: 'App\SomeClass' }
+                    - { name: 'container.preload', class: 'App\Some\OtherClass' }
+                    # ...
+
+    .. code-block:: xml
+
+        <?xml version="1.0" encoding="UTF-8" ?>
+        <container xmlns="http://symfony.com/schema/dic/services"
+            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+            xsi:schemaLocation="http://symfony.com/schema/dic/services
+                https://symfony.com/schema/dic/services/services-1.0.xsd">
+
+            <services>
+                <service id="App\SomeNamespace\SomeService">
+                    <tag name="container.preload" class="App\SomeClass"/>
+                    <tag name="container.preload" class="App\Some\OtherClass"/>
+                    <!-- ... -->
+                </service>
+            </services>
+        </container>
+
+    .. code-block:: php
+
+        use App\Some\OtherClass;
+        use App\SomeClass;
+        use App\SomeNamespace\SomeService;
+
+        $container
+            ->register(SomeService::class)
+            ->addTag('container.preload', ['class' => SomeClass::class)
+            ->addTag('container.preload', ['class' => OtherClass::class)
+            // ...
+        ;
+
 controller.argument_value_resolver
 ----------------------------------
 
@@ -1214,3 +1319,4 @@ Bridge.
 .. _`Twig's documentation`: https://twig.symfony.com/doc/2.x/advanced.html#creating-an-extension
 .. _`SwiftMailer's Plugin Documentation`: https://swiftmailer.symfony.com/docs/plugins.html
 .. _`Twig Loader`: https://twig.symfony.com/doc/2.x/api.html#loaders
+.. _`PHP class preloading`: https://www.php.net/manual/en/opcache.configuration.php#ini.opcache.preload