[3.13] GH-124567: Revert the Incremental GC in 3.13 (#124770)

Revert the incremental GC in 3.13, since it's not clear that without further turning, the benefits outweigh the costs.

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>

1 files changed, 15 insertions, 10 deletions

diff --git a/Modules/gcmodule.c b/Modules/gcmodule.c
index 57e4aae..b57a1c9 100644
--- a/Modules/gcmodule.c
+++ b/Modules/gcmodule.c
@@ -158,12 +158,17 @@ gc_set_threshold_impl(PyObject *module, int threshold0, int group_right_1,
 {
     GCState *gcstate = get_gc_state();
 
-    gcstate->young.threshold = threshold0;
+    gcstate->generations[0].threshold = threshold0;
     if (group_right_1) {
-        gcstate->old[0].threshold = threshold1;
+        gcstate->generations[1].threshold = threshold1;
     }
     if (group_right_2) {
-        gcstate->old[1].threshold = threshold2;
+        gcstate->generations[2].threshold = threshold2;
+
+        /* generations higher than 2 get the same threshold */
+        for (int i = 3; i < NUM_GENERATIONS; i++) {
+            gcstate->generations[i].threshold = gcstate->generations[2].threshold;
+        }
     }
     Py_RETURN_NONE;
 }
@@ -180,9 +185,9 @@ gc_get_threshold_impl(PyObject *module)
 {
     GCState *gcstate = get_gc_state();
     return Py_BuildValue("(iii)",
-                         gcstate->young.threshold,
-                         gcstate->old[0].threshold,
-                         0);
+                         gcstate->generations[0].threshold,
+                         gcstate->generations[1].threshold,
+                         gcstate->generations[2].threshold);
 }
 
 /*[clinic input]
@@ -202,14 +207,14 @@ gc_get_count_impl(PyObject *module)
     struct _gc_thread_state *gc = &tstate->gc;
 
     // Flush the local allocation count to the global count
-    _Py_atomic_add_int(&gcstate->young.count, (int)gc->alloc_count);
+    _Py_atomic_add_int(&gcstate->generations[0].count, (int)gc->alloc_count);
     gc->alloc_count = 0;
 #endif
 
     return Py_BuildValue("(iii)",
-                         gcstate->young.count,
-                         gcstate->old[gcstate->visited_space].count,
-                         gcstate->old[gcstate->visited_space^1].count);
+                         gcstate->generations[0].count,
+                         gcstate->generations[1].count,
+                         gcstate->generations[2].count);
 }
 
 /*[clinic input]