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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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Fix allocation count decrement and GC state update 
Adjust allocation count handling to prevent negative values and update GC state accordingly.
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@kevmo314
kevmo314 authored Dec 1, 2025
commit 9388518613c625629ca3f289561743f7fd952de1
21 changes: 17 additions & 4 deletions Python/gc_free_threading.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2207,10 +2207,23 @@ record_deallocation(PyThreadState *tstate)
{
struct _gc_thread_state *gc = &((_PyThreadStateImpl *)tstate)->gc;

// 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--;
gc->alloc_count--;
if (gc->alloc_count <= -LOCAL_ALLOC_COUNT_THRESHOLD) {
GCState *gcstate = &tstate->interp->gc;
int count = _Py_atomic_load_int_relaxed(&gcstate->young.count);
int new_count;
do {
if (count == 0){
break;
}
new_count = count + (int)gc->alloc_count;
if (new_count < 0) {
new_count = 0;
}
} while (!_Py_atomic_compare_exchange_int(&gcstate->young.count,
&count,
new_count));
gc->alloc_count = 0;
}
}

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