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GH-139951: Fix major GC performance regression (GH-140262)

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* Count number of actually tracked objects, instead of trackable objects. This ensures that untracking tuples has the desired effect of reducing GC overhead

* Do not track most untrackable tuples during creation. This prevents large numbers of small tuples causing execessive GCs.
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Mark Shannon 2025-10-21 15:22:15 +01:00 • committed by GitHub
parent 4adf08ae46
commit 0c01090ad9
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5 changed files with 93 additions and 36 deletions
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43
Python/gc.c
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@ -1639,7 +1639,7 @@ assess_work_to_do(GCState *gcstate)
scale_factor = 2;
}
intptr_t new_objects = gcstate->young.count;
intptr_t max_heap_fraction = new_objects*3/2;
intptr_t max_heap_fraction = new_objects*2;
intptr_t heap_fraction = gcstate->heap_size / SCAN_RATE_DIVISOR / scale_factor;
if (heap_fraction > max_heap_fraction) {
heap_fraction = max_heap_fraction;
@ -1654,6 +1654,9 @@ gc_collect_increment(PyThreadState *tstate, struct gc_collection_stats *stats)
GC_STAT_ADD(1, collections, 1);
GCState *gcstate = &tstate->interp->gc;
gcstate->work_to_do += assess_work_to_do(gcstate);
if (gcstate->work_to_do < 0) {
return;
}
untrack_tuples(&gcstate->young.head);
if (gcstate->phase == GC_PHASE_MARK) {
Py_ssize_t objects_marked = mark_at_start(tstate);
@ -1696,7 +1699,6 @@ gc_collect_increment(PyThreadState *tstate, struct gc_collection_stats *stats)
gc_collect_region(tstate, &increment, &survivors, stats);
gc_list_merge(&survivors, visited);
assert(gc_list_is_empty(&increment));
gcstate->work_to_do += gcstate->heap_size / SCAN_RATE_DIVISOR / scale_factor;
gcstate->work_to_do -= increment_size;
add_stats(gcstate, 1, stats);
@ -2299,21 +2301,11 @@ _Py_ScheduleGC(PyThreadState *tstate)
}
void
_PyObject_GC_Link(PyObject *op)
_Py_TriggerGC(struct _gc_runtime_state *gcstate)
{
PyGC_Head *gc = AS_GC(op);
// gc must be correctly aligned
_PyObject_ASSERT(op, ((uintptr_t)gc & (sizeof(uintptr_t)-1)) == 0);
PyThreadState *tstate = _PyThreadState_GET();
GCState *gcstate = &tstate->interp->gc;
gc->_gc_next = 0;
gc->_gc_prev = 0;
gcstate->young.count++; /* number of allocated GC objects */
gcstate->heap_size++;
if (gcstate->young.count > gcstate->young.threshold &&
gcstate->enabled &&
gcstate->young.threshold &&
if (gcstate->enabled &&
gcstate->young.threshold != 0 &&
!_Py_atomic_load_int_relaxed(&gcstate->collecting) &&
!_PyErr_Occurred(tstate))
{
@ -2321,6 +2313,17 @@ _PyObject_GC_Link(PyObject *op)
}
}
void
_PyObject_GC_Link(PyObject *op)
{
PyGC_Head *gc = AS_GC(op);
// gc must be correctly aligned
_PyObject_ASSERT(op, ((uintptr_t)gc & (sizeof(uintptr_t)-1)) == 0);
gc->_gc_next = 0;
gc->_gc_prev = 0;
}
void
_Py_RunGC(PyThreadState *tstate)
{
@ -2427,6 +2430,11 @@ PyObject_GC_Del(void *op)
PyGC_Head *g = AS_GC(op);
if (_PyObject_GC_IS_TRACKED(op)) {
gc_list_remove(g);
GCState *gcstate = get_gc_state();
if (gcstate->young.count > 0) {
gcstate->young.count--;
}
gcstate->heap_size--;
#ifdef Py_DEBUG
PyObject *exc = PyErr_GetRaisedException();
if (PyErr_WarnExplicitFormat(PyExc_ResourceWarning, "gc", 0,
@ -2440,11 +2448,6 @@ PyObject_GC_Del(void *op)
PyErr_SetRaisedException(exc);
#endif
}
GCState *gcstate = get_gc_state();
if (gcstate->young.count > 0) {
gcstate->young.count--;
}
gcstate->heap_size--;
PyObject_Free(((char *)op)-presize);
}