[3.14] GH-133136: Revise QSBR to reduce excess memory held (gh-135473) (#135912)

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 commit 113de8545f)

Co-authored-by: Neil Schemenauer <nas-github@arctrix.com>
Co-authored-by: Sam Gross <colesbury@gmail.com>
This commit is contained in:
Miss Islington (bot) 2025-07-08 19:58:01 +02:00 committed by GitHub
parent 66f85f4be8
commit 6a2a2906f8
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10 changed files with 3530 additions and 3422 deletions

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@ -3368,7 +3368,7 @@ create_tlbc_lock_held(PyCodeObject *co, Py_ssize_t idx)
}
memcpy(new_tlbc->entries, tlbc->entries, tlbc->size * sizeof(void *));
_Py_atomic_store_ptr_release(&co->co_tlbc, new_tlbc);
_PyMem_FreeDelayed(tlbc);
_PyMem_FreeDelayed(tlbc, tlbc->size * sizeof(void *));
tlbc = new_tlbc;
}
char *bc = PyMem_Calloc(1, _PyCode_NBYTES(co));