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GH-139951: Fix major GC performance regression - #140262
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markshannon merged 6 commits intoOct 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.
eendebakpt
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Oct 17, 2025
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Objects/tupleobject.c
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Python/gc.c
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Include/internal/pycore_gc.h
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Python/gc.c
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Include/internal/pycore_gc.h
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Python/gc.c
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I'm not sure I get what android (x86_64) fails.
if (gcstate->work_to_do < 0) {
return;
}
|
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I'm not at all familiar with the garbage collector, but one of the ways that Android differs from the other platforms is that it runs all the test suite serially in a single process. |
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Python/gc.c
sergey-miryanov
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Oct 21, 2025
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Code looks good to me, thanks!
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Should we redo the benchmarks to see how the final version impacts performance? Maybe we can run it on https://github.com/faster-cpython/benchmarking-public (but I don't know how). |
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efimov-mikhail
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Oct 21, 2025
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Include/internal/pycore_gc.h
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Misc/NEWS.d/next/Core_and_Builtins/2025-10-17-18-03-12.gh-issue-139951.IdwM2O.rst
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Thanks @markshannon for the PR 🌮🎉.. I'm working now to backport this PR to: 3.14. |
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miss-islington
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Oct 21, 2025
* 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>
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GH-140423 is a backport of this pull request to the 3.14 branch. |
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markshannon
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Oct 23, 2025
…-140262 (GH-140447) * 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.
This was referenced Oct 25, 2025
nascheme
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Nov 27, 2025
This reverts parts of the pythonGH-140262 change. The changes that affect the tuple untracking are left unchanged. Revert the changes to the calculation of the increment size, based on the "work_to_do" variable. This causes cyclic garbage to be collected more quickly. Revert also the change to test_gc.py, which was done because the expected GC collection was taking longer to happen. With the tuple untrack change, the performance regression as reported by bug pythonGH-139951 is still resolved (work_to_do changes are not required).
This was referenced Nov 27, 2025
StanFromIreland
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Dec 6, 2025
* 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.
sergey-miryanov
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Jan 24, 2026
This reverts parts of the pythonGH-140262 change. The changes that affect the tuple untracking are left unchanged. Revert the changes to the calculation of the increment size, based on the "work_to_do" variable. This causes cyclic garbage to be collected more quickly. Revert also the change to test_gc.py, which was done because the expected GC collection was taking longer to happen. With the tuple untrack change, the performance regression as reported by bug pythonGH-139951 is still resolved (work_to_do changes are not required).
sergey-miryanov
pushed a commit
to sergey-miryanov/cpython
that referenced
this pull request
Jan 25, 2026
This reverts parts of the pythonGH-140262 change. The changes that affect the tuple untracking are left unchanged. Revert the changes to the calculation of the increment size, based on the "work_to_do" variable. This causes cyclic garbage to be collected more quickly. Revert also the change to test_gc.py, which was done because the expected GC collection was taking longer to happen. With the tuple untrack change, the performance regression as reported by bug pythonGH-139951 is still resolved (work_to_do changes are not required).
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This PR:
For the example in the original report this makes performance on main a bit better than 3.13.
Benchmarking results show this is about neutral on performance otherwise.