Address review comments

Author: markshannon

Include/internal/pycore_gc.h

@@ -253,7 +253,7 @@ static inline void _PyObject_GC_TRACK(
     uintptr_t not_visited = 1 ^ gcstate->visited_space;
     gc->_gc_next = ((uintptr_t)generation0) | not_visited;
     generation0->_gc_prev = (uintptr_t)gc;
-    gcstate->young.count++; /* number of allocated GC objects */
+    gcstate->young.count++; /* number of tracked GC objects */
     gcstate->heap_size++;
     if (gcstate->young.count > gcstate->young.threshold) {
         _Py_TriggerGC(gcstate);

Objects/tupleobject.c

@@ -158,7 +158,7 @@ _PyTuple_MaybeUntrack(PyObject *op)
 
 /* Fast, but conservative check if an object maybe tracked
    May return true for an object that is not tracked,
-   Will alwys return true for an object that is tracked.
+   Will always return true for an object that is tracked.
    This is a temporary workaround until _PyObject_GC_IS_TRACKED
    becomes fast and safe to call on non-GC objects.
 */

Python/gc.c

@@ -1657,6 +1657,8 @@ gc_collect_increment(PyThreadState *tstate, struct gc_collection_stats *stats)
     if (gcstate->work_to_do < 0) {
         return;
     }
+    /* untrack_tuples() may reduce gcstate->young.count to less than zero.
+       This is harmless as it will merely delay the next GC a bit. */
     untrack_tuples(&gcstate->young.head);
     if (gcstate->phase == GC_PHASE_MARK) {
         Py_ssize_t objects_marked = mark_at_start(tstate);
@@ -2292,6 +2294,7 @@ _Py_TriggerGC(struct _gc_runtime_state *gcstate)
 {
     PyThreadState *tstate = _PyThreadState_GET();
     if (gcstate->enabled &&
+        gcstate->young.threshold != 0 &&
         !_Py_atomic_load_int_relaxed(&gcstate->collecting) &&
         !_PyErr_Occurred(tstate))
     {