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[3.14] GH-133136: Revise QSBR to reduce excess memory held (gh-135473)#135912
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…35473)The free threading build uses QSBR to delay the freeing of dictionarykeys and list arrays when the objects are accessed by multiple threadsin order to allow concurrent reads to proceed with holding the objectlock. The requests are processed in batches to reduce executionoverhead, but for large memory blocks this can lead to excess memoryusage.Take into account the size of the memory block when deciding when toprocess QSBR requests.Also track the amount of memory being held by QSBR for mimalloc pages. Advance the write sequence if this memory exceeds a limit. Advancing the sequence will allow it to be freed more quickly.Process the held QSBR items from the "eval breaker", rather than from `_PyMem_FreeDelayed()`. This gives a higher chance that the global read sequence has advanced enough so that items can be freed.(cherry picked from commit113de85)Co-authored-by: Neil Schemenauer <nas-github@arctrix.com>Co-authored-by: Sam Gross <colesbury@gmail.com>
bedevere-bot commentedJun 25, 2025
🤖 New build scheduled with the buildbot fleet by@nascheme for commitd7d6412 🤖 Results will be shown at: https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F135912%2Fmerge If you want to schedule another build, you need to add the🔨 test-with-buildbots label again. |
@hugovk I understand this needs review by the release manager due to the potential ABI change. Ibelieve this change is okay. The |
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The free threading build uses QSBR to delay the freeing of dictionary
keys and list arrays when the objects are accessed by multiple threads
in order to allow concurrent reads to proceed with holding the object
lock. The requests are processed in batches to reduce execution
overhead, but for large memory blocks this can lead to excess memory
usage.
Take into account the size of the memory block when deciding when to
process QSBR requests.
Also track the amount of memory being held by QSBR for mimalloc pages. Advance the write sequence if this memory exceeds a limit. Advancing the sequence will allow it to be freed more quickly.
Process the held QSBR items from the "eval breaker", rather than from
_PyMem_FreeDelayed(). This gives a higher chance that the global read sequence has advanced enough so that items can be freed.(cherry picked from commit113de85)
Co-authored-by: Neil Schemenauernas-github@arctrix.com
Co-authored-by: Sam Grosscolesbury@gmail.com