Implemented Martin's suggestion to clear the free lists during the garbage collection of the highest generation.
diff --git a/Misc/NEWS b/Misc/NEWS
index fe4b89f..134ac7e 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,10 @@
Core and builtins
-----------------
+- Clear all free list during a gc.collect() of the highest generation in order
+ to allow pymalloc to free more arenas. Python may give back memory to the
+ OS earlier.
+
- Issue #2045: Fix an infinite recursion triggered when printing a subclass of
collections.defaultdict, if its default_factory is set to a bound method.