gh-81381: Reduce allcoated size of PyType_GenericAlloc if possible

corona10 · corona10 · commit 3946154dde06 · 2023-01-09T00:55:16.000+09:00
diff --git a/Misc/NEWS.d/next/Core and Builtins/2023-01-09-00-55-03.gh-issue-81381.21bU3z.rst b/Misc/NEWS.d/next/Core and Builtins/2023-01-09-00-55-03.gh-issue-81381.21bU3z.rst
@@ -0,0 +1,2 @@
+Reduce the extra allocation size of :c:func:`PyType_GenericAlloc` except the
+type is if a subtype of 'type'.
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
@@ -1289,9 +1289,12 @@ PyObject *
 _PyType_AllocNoTrack(PyTypeObject *type, Py_ssize_t nitems)
 {
     PyObject *obj;
-    const size_t size = _PyObject_VAR_SIZE(type, nitems+1);
-    /* note that we need to add one, for the sentinel */
-
+    size_t extra = 0;
+    if (type->tp_flags & Py_TPFLAGS_TYPE_SUBCLASS) {
+        /* note that we need to add one, for the sentinel */
+        extra = 1;
+    }
+    const size_t size = _PyObject_VAR_SIZE(type, nitems + extra);
     const size_t presize = _PyType_PreHeaderSize(type);
     char *alloc = PyObject_Malloc(size + presize);
     if (alloc  == NULL) {

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+Reduce the extra allocation size of :c:func:`PyType_GenericAlloc` except the
	`2`	`+type is if a subtype of 'type'.`