diff --git a/src/greenlet/greenlet.cpp b/src/greenlet/greenlet.cpp
index a05ca7c3..5a903bf4 100644
--- a/src/greenlet/greenlet.cpp
+++ b/src/greenlet/greenlet.cpp
@@ -2911,6 +2911,20 @@ greenlet_internal_mod_init() G_NOEXCEPT
                                                NULL)));
         m.PyAddObject("_C_API", c_api_object);
         assert(c_api_object.REFCNT() == 2);
+
+        // cerr << "Sizes:"
+        //      << "\n\tGreenlet       : " << sizeof(Greenlet)
+        //      << "\n\tUserGreenlet   : " << sizeof(UserGreenlet)
+        //      << "\n\tMainGreenlet   : " << sizeof(MainGreenlet)
+        //      << "\n\tExceptionState : " << sizeof(greenlet::ExceptionState)
+        //      << "\n\tPythonState    : " << sizeof(greenlet::PythonState)
+        //      << "\n\tStackState     : " << sizeof(greenlet::StackState)
+        //      << "\n\tSwitchingArgs  : " << sizeof(greenlet::SwitchingArgs)
+        //      << "\n\tOwnedObject    : " << sizeof(greenlet::refs::OwnedObject)
+        //      << "\n\tBorrowedObject : " << sizeof(greenlet::refs::BorrowedObject)
+        //      << "\n\tPyGreenlet     : " << sizeof(PyGreenlet)
+        //      << endl;
+
         return m.borrow(); // But really it's the main reference.
     }
     catch (const LockInitError& e) {
diff --git a/src/greenlet/greenlet_greenlet.hpp b/src/greenlet/greenlet_greenlet.hpp
index 2d496d9d..60c1d829 100644
--- a/src/greenlet/greenlet_greenlet.hpp
+++ b/src/greenlet/greenlet_greenlet.hpp
@@ -16,6 +16,9 @@ using greenlet::refs::OwnedGreenlet;
 using greenlet::refs::OwnedMainGreenlet;
 using greenlet::refs::BorrowedGreenlet;
 
+// XXX: TODO: Work to remove all virtual functions
+// for speed of calling and size of objects (no vtable).
+// One pattern is the Curiously Recurring Template
 namespace greenlet
 {
     class ExceptionState