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gh-81381: Reduce allocated size of PyType_GenericAlloc if possible #100855

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gh-81381: Reduce allocated size of PyType_GenericAlloc if possible #100855

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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2023-01-09-00-55-03.gh-issue-81381.21bU3z.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Reduce the extra allocation size of :c:func:`PyType_GenericAlloc` except the
type is if a subtype of 'type'.
11 changes: 7 additions & 4 deletions Objects/typeobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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 || type->tp_flags & Py_TPFLAGS_HAVE_VECTORCALL) {
/* 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) {
Expand All @@ -1309,7 +1312,7 @@ _PyType_AllocNoTrack(PyTypeObject *type, Py_ssize_t nitems)
_PyObject_Init(obj, type);
}
else {
_PyObject_InitVar((PyVarObject *)obj, type, nitems);
_PyObject_InitVar((PyVarObject *)obj, type, nitems + extra);
}
return obj;
}
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