gh-133136: Limit excess memory held by QSBR

Include/internal/pycore_pymem.h

@@ -88,7 +88,7 @@ extern wchar_t *_PyMem_DefaultRawWcsdup(const wchar_t *str);
 extern int _PyMem_DebugEnabled(void);
 
 // Enqueue a pointer to be freed possibly after some delay.
-extern void _PyMem_FreeDelayed(void *ptr);
+extern void _PyMem_FreeDelayed(void *ptr, size_t size);
 
 // Enqueue an object to be freed possibly after some delay
 #ifdef Py_GIL_DISABLED

Include/internal/pycore_qsbr.h

@@ -51,6 +51,10 @@ struct _qsbr_thread_state {
     // Used to defer advancing write sequence a fixed number of times
     int deferrals;
 
+    // Estimate for the amount of memory that is held by this thread since
+    // the last non-deferred advance.
+    size_t memory_deferred;
+
     // Is this thread state allocated?
     bool allocated;
     struct _qsbr_thread_state *freelist_next;

Misc/NEWS.d/next/Core_and_Builtins/2025-06-03-21-06-22.gh-issue-133136.Usnvri.rst

@@ -0,0 +1,2 @@
+Limit excess memory usage in the :term:`free threading` build when a
+large dictionary or list is resized and accessed by multiple threads.

Objects/codeobject.c

@@ -3350,7 +3350,7 @@ create_tlbc_lock_held(PyCodeObject *co, Py_ssize_t idx)
         }
         memcpy(new_tlbc->entries, tlbc->entries, tlbc->size * sizeof(void *));
         _Py_atomic_store_ptr_release(&co->co_tlbc, new_tlbc);
-        _PyMem_FreeDelayed(tlbc);
+        _PyMem_FreeDelayed(tlbc, tlbc->size * sizeof(void *));
         tlbc = new_tlbc;
     }
     char *bc = PyMem_Calloc(1, _PyCode_NBYTES(co));

Objects/dictobject.c

@@ -813,7 +813,7 @@ free_keys_object(PyDictKeysObject *keys, bool use_qsbr)
 {
 #ifdef Py_GIL_DISABLED
     if (use_qsbr) {
-        _PyMem_FreeDelayed(keys);
+        _PyMem_FreeDelayed(keys, _PyDict_KeysSize(keys));
         return;
     }
 #endif
@@ -858,7 +858,7 @@ free_values(PyDictValues *values, bool use_qsbr)
     assert(values->embedded == 0);
 #ifdef Py_GIL_DISABLED
     if (use_qsbr) {
-        _PyMem_FreeDelayed(values);
+        _PyMem_FreeDelayed(values, values_size_from_count(values->capacity));
         return;
     }
 #endif

Objects/listobject.c

@@ -61,7 +61,8 @@ free_list_items(PyObject** items, bool use_qsbr)
 #ifdef Py_GIL_DISABLED
     _PyListArray *array = _Py_CONTAINER_OF(items, _PyListArray, ob_item);
     if (use_qsbr) {
-        _PyMem_FreeDelayed(array);
+        size_t size = sizeof(_PyListArray) + array->allocated * sizeof(PyObject *);
+        _PyMem_FreeDelayed(array, size);
     }
     else {
         PyMem_Free(array);

Objects/obmalloc.c

@@ -1141,8 +1141,29 @@ free_work_item(uintptr_t ptr, delayed_dealloc_cb cb, void *state)
     }
 }
 
+#ifdef Py_GIL_DISABLED
+static int
+should_advance_qsbr(_PyThreadStateImpl *tstate, size_t size)
+{
+    // If the deferred memory exceeds 1 MiB, we force an advance in the
+    // shared QSBR sequence number to limit excess memory usage.
+    static const size_t QSBR_DEFERRED_LIMIT = 1024 * 1024;
+    if (size > QSBR_DEFERRED_LIMIT) {
+        tstate->qsbr->memory_deferred = 0;
+        return 1;
+    }
+
+    tstate->qsbr->memory_deferred += size;
+    if (tstate->qsbr->memory_deferred > QSBR_DEFERRED_LIMIT) {
+        tstate->qsbr->memory_deferred = 0;
+        return 1;
+    }
+    return 0;
+}
+#endif
+
 static void
-free_delayed(uintptr_t ptr)
+free_delayed(uintptr_t ptr, size_t size)
 {
 #ifndef Py_GIL_DISABLED
     free_work_item(ptr, NULL, NULL);
@@ -1200,23 +1221,29 @@ free_delayed(uintptr_t ptr)
     }
 
     assert(buf != NULL && buf->wr_idx < WORK_ITEMS_PER_CHUNK);
-    uint64_t seq = _Py_qsbr_deferred_advance(tstate->qsbr);
+    uint64_t seq;
+    int force_advance = should_advance_qsbr(tstate, size);
+    if (force_advance) {
+        seq = _Py_qsbr_advance(tstate->qsbr->shared);
+    }
+    else {
+        seq = _Py_qsbr_deferred_advance(tstate->qsbr);
+    }
     buf->array[buf->wr_idx].ptr = ptr;
     buf->array[buf->wr_idx].qsbr_goal = seq;
     buf->wr_idx++;
-
-    if (buf->wr_idx == WORK_ITEMS_PER_CHUNK) {
+    if (buf->wr_idx == WORK_ITEMS_PER_CHUNK || force_advance) {
         _PyMem_ProcessDelayed((PyThreadState *)tstate);
     }
 #endif
 }
 
 void
-_PyMem_FreeDelayed(void *ptr)
+_PyMem_FreeDelayed(void *ptr, size_t size)
 {
     assert(!((uintptr_t)ptr & 0x01));
     if (ptr != NULL) {
-        free_delayed((uintptr_t)ptr);
+        free_delayed((uintptr_t)ptr, size);
     }
 }
 
@@ -1226,7 +1253,7 @@ _PyObject_XDecRefDelayed(PyObject *ptr)
 {
     assert(!((uintptr_t)ptr & 0x01));
     if (ptr != NULL) {
-        free_delayed(((uintptr_t)ptr)|0x01);
+        free_delayed(((uintptr_t)ptr)|0x01, 64);
     }
 }
 #endif