cpython/Python/gc_gil.c

#include "Python.h"
#include "pycore_freelist.h"   // _PyObject_ClearFreeLists()

#ifndef Py_GIL_DISABLED

/* Clear all free lists
 * All free lists are cleared during the collection of the highest generation.
 * Allocated items in the free list may keep a pymalloc arena occupied.
 * Clearing the free lists may give back memory to the OS earlier.
 */
void
_PyGC_ClearAllFreeLists(PyInterpreterState *interp)
{ … }

#endif