WIP

Include/internal/pycore_gc.h

@@ -312,6 +312,10 @@ struct _gc_runtime_state {
        collections, and are awaiting to undergo a full collection for
        the first time. */
     Py_ssize_t long_lived_pending;
+
+    /* True to use immortalization in places where we would normally use
+       deferred reference counting. */
+    int immortalize_deferred;
 #endif
 };
 
@@ -343,6 +347,11 @@ extern void _PyGC_ClearAllFreeLists(PyInterpreterState *interp);
 extern void _Py_ScheduleGC(PyThreadState *tstate);
 extern void _Py_RunGC(PyThreadState *tstate);
 
+#ifdef Py_GIL_DISABLED
+// gh-117783: Immortalize objects that use deferred reference counting
+extern void _PyGC_ImmortalizeDeferredObjects(PyInterpreterState *interp);
+#endif
+
 #ifdef __cplusplus
 }
 #endif

Objects/object.c

@@ -2430,7 +2430,13 @@ _PyObject_SetDeferredRefcount(PyObject *op)
 #ifdef Py_GIL_DISABLED
     assert(PyType_IS_GC(Py_TYPE(op)));
     assert(_Py_IsOwnedByCurrentThread(op));
-    assert( op->ob_ref_shared == 0);
+    assert(op->ob_ref_shared == 0);
+    PyInterpreterState *interp = _PyInterpreterState_GET();
+    if (interp->gc.immortalize_deferred) {
+        // gh-117696: 
+        _Py_SetImmortal(op);
+        return;
+    }
     op->ob_gc_bits |= _PyGC_BITS_DEFERRED;
     op->ob_ref_local += 1;
     op->ob_ref_shared = _Py_REF_QUEUED;

Python/gc_free_threading.c

@@ -1781,6 +1781,30 @@ custom_visitor_wrapper(const mi_heap_t *heap, const mi_heap_area_t *area,
     return true;
 }
 
+// gh-117783: Immortalize objects that use deferred reference counting to
+// temporarily work around scaling bottlenecks.
+static bool
+immortalize_visitor(const mi_heap_t *heap, const mi_heap_area_t *area,
+                    void *block, size_t block_size, void *args)
+{
+    PyObject *op = op_from_block(block, args, false);
+    if (op != NULL && _PyObject_HasDeferredRefcount(op)) {
+        _Py_SetImmortal(op);
+        op->ob_gc_bits &= ~_PyGC_BITS_DEFERRED;
+    }
+    return true;
+}
+
+void
+_PyGC_ImmortalizeDeferredObjects(PyInterpreterState *interp)
+{
+    struct visitor_args args;
+    _PyEval_StopTheWorld(interp);
+    gc_visit_heaps(interp, &immortalize_visitor, &args);
+    interp->gc.immortalize_deferred = 1;
+    _PyEval_StartTheWorld(interp);
+}
+
 void
 PyUnstable_GC_VisitObjects(gcvisitobjects_t callback, void *arg)
 {

Python/pystate.c

@@ -1565,6 +1565,13 @@ new_threadstate(PyInterpreterState *interp, int whence)
         // Must be called with lock unlocked to avoid re-entrancy deadlock.
         PyMem_RawFree(new_tstate);
     }
+    else {
+#ifdef Py_GIL_DISABLED
+        if (!interp->gc.immortalize_deferred) {
+            _PyGC_ImmortalizeDeferredObjects(interp);
+        }
+#endif
+    }
 
 #ifdef Py_GIL_DISABLED
     // Must be called with lock unlocked to avoid lock ordering deadlocks.