Add description of marshal changes.
diff --git a/Doc/whatsnew/3.4.rst b/Doc/whatsnew/3.4.rst
index a894bcd..5c9511f 100644
--- a/Doc/whatsnew/3.4.rst
+++ b/Doc/whatsnew/3.4.rst
@@ -131,7 +131,8 @@
* :ref:`Secure and interchangeable hash algorithm <whatsnew-pep-456>`
(:pep:`456`).
* :ref:`Argument Clinic <whatsnew-pep-436>` (:pep:`436`).
-* A more efficient :mod:`marshal` format (:issue:`16475`).
+* The :mod:`marshal` format has been made :ref:`more compact and efficient
+ <whatsnew-marshal-3>` (:issue:`16475`).
Please read on for a comprehensive list of user-facing changes.
@@ -626,6 +627,20 @@
:issue:`19030`)
+.. _whatsnew-marshal-3:
+
+marshal
+-------
+
+The default :mod:`marshal` version has been bumped to 3. The code implementing
+the new version restores the Python2 behavior of recording only one copy of
+interned strings and preserving the interning on deserialization, and extends
+this "one copy" ability to any object type (including handling recursive
+references). This reduces both the size of ``.pyc`` files and the amount of
+memory a module occupies in memory when it is loaded from a ``.pyc`` (or
+``.pyo``) file. (Contributed by Kristján Valur Jónsson in :issue:`16475`.)
+
+
mmap
----