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gh-142048: Fix quadratically increasing GC delays #142051

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Merged
colesbury merged 8 commits into from
Dec 2, 2025
Merged

gh-142048: Fix quadratically increasing GC delays #142051

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a9edb7b
reset allocation counts in gc thread-local buffers
kevmo314 Nov 28, 2025
b1a6c16
Merge branch 'main' into fix-gc-alloc-count-negative
kevmo314 Nov 30, 2025
9388518
Fix allocation count decrement and GC state update
kevmo314 Dec 1, 2025
f5e46b5
Fix formatting in gc_free_threading.c
kevmo314 Dec 1, 2025
795e703
Update Python/pystate.c
kevmo314 Dec 1, 2025
8d01b65
news and lint
kevmo314 Dec 1, 2025
8be49b5
Remove local GC allocation count flush in pystate.c
kevmo314 Dec 1, 2025
f202991
Merge branch 'main' into fix-gc-alloc-count-negative
kevmo314 Dec 1, 2025
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reset allocation counts in gc thread-local buffers
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@kevmo314
kevmo314 committed Nov 28, 2025
commit a9edb7b7974507c7ae23dfbd8edd7c0025e74a5a
9 changes: 4 additions & 5 deletions Python/gc_free_threading.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2207,11 +2207,10 @@ record_deallocation(PyThreadState *tstate)
{
struct _gc_thread_state *gc = &((_PyThreadStateImpl *)tstate)->gc;

gc->alloc_count--;
if (gc->alloc_count <= -LOCAL_ALLOC_COUNT_THRESHOLD) {
GCState *gcstate = &tstate->interp->gc;
_Py_atomic_add_int(&gcstate->young.count, (int)gc->alloc_count);
gc->alloc_count = 0;
// Only decrement if positive, matching gc.c behavior which prevents
// negative counts (see PyObject_GC_Del in gc.c).
if (gc->alloc_count > 0) {
gc->alloc_count--;
}
}

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8 changes: 8 additions & 0 deletions Python/pystate.c
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Expand Up @@ -1810,6 +1810,14 @@ tstate_delete_common(PyThreadState *tstate, int release_gil)
assert(tstate_impl->refcounts.values == NULL);
#endif

#ifdef Py_GIL_DISABLED
// Flush the thread's local GC allocation count to the global count
// before the thread state is deleted, otherwise the count is lost.
_Py_atomic_add_int(&tstate->interp->gc.young.count,
(int)((_PyThreadStateImpl *)tstate)->gc.alloc_count);
((_PyThreadStateImpl *)tstate)->gc.alloc_count = 0;
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#endif

#if _Py_TIER2
_PyThreadStateImpl *_tstate = (_PyThreadStateImpl *)tstate;
if (_tstate->jit_tracer_state.code_buffer != NULL) {
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