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[3.14] GH-139951: Fix major GC performance regression (GH-140262)#140423

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[3.14] GH-139951: Fix major GC performance regression (GH-140262)#140423
miss-islington wants to merge 1 commit into
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@miss-islington

@miss-islington miss-islington commented Oct 21, 2025

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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.
    (cherry picked from commit 0c01090)

Co-authored-by: Mark Shannon mark@hotpy.org

* 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.
(cherry picked from commit 0c01090)

Co-authored-by: Mark Shannon <mark@hotpy.org>
@sergey-miryanov

sergey-miryanov commented Oct 21, 2025

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The following change fixes free-threading tests (mainly -1386,10 +1385,6 fixes tests, other is a cleanup):

diff --git a/Lib/test/test_gc.py b/Lib/test/test_gc.py
index db643330894..d7a4c066437 100644
--- a/Lib/test/test_gc.py
+++ b/Lib/test/test_gc.py
@@ -3,8 +3,7 @@
 from test import support
 from test.support import (verbose, refcount_test,
                           cpython_only, requires_subprocess,
-                          requires_gil_enabled,
-                          Py_GIL_DISABLED)
+                          requires_gil_enabled)
 from test.support.import_helper import import_module
 from test.support.os_helper import temp_dir, TESTFN, unlink
 from test.support.script_helper import assert_python_ok, make_script, run_test_script
@@ -1386,10 +1385,6 @@ def callback(ignored):
         junk = []
         i = 0
         detector = GC_Detector()
-        if Py_GIL_DISABLED:
-            # The free-threaded build doesn't have multiple generations, so
-            # just trigger a GC manually.
-            gc.collect()
         assert not detector.gc_happened
         while not detector.gc_happened:
             i += 1
@@ -1459,10 +1454,6 @@ def __del__(self):
         detector = GC_Detector()
         junk = []
         i = 0
-        if Py_GIL_DISABLED:
-            # The free-threaded build doesn't have multiple generations, so
-            # just trigger a GC manually.
-            gc.collect()
         while not detector.gc_happened:
             i += 1
             if i > 50000:

Is it fine if I add such commit to this PR? Should we apply this change to the main?

@efimov-mikhail

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Сс @colesbury

@colesbury

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The test has a @unittest.skipIf(Py_GIL_DISABLED, "requires GC generations or increments") on main, it should have the same on 3.14

@markshannon

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Closing in favor of #140447

@miss-islington miss-islington deleted the backport-0c01090-3.14 branch January 2, 2026 16:39
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