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Free pages awaiting QSBR are added to each thread's `mimalloc.page_list`. The list is only drained if the owning thread needs new pages, performs an allocation larger than mimalloc's medium-object limit, or the thread exits. This means that we don't free pages if a thread's allocation pattern quiesces or falls into a pattern that can be serviced by existing pages. This can be problematic for threads that allocate a bunch of memory and then settle into the previous pattern.
Add _testinternalcapi.get_qsbr_page_list_length(), which counts the pages on all threads' QSBR page lists, and use it to check that gc.collect() frees empty pages parked by the calling thread and by an idle thread. Also check that the GC skips thread states that have not initialized their mimalloc state yet.
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Hmm let me take a look also!
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Free pages awaiting QSBR are added to each thread's
mimalloc.page_list.The list is only drained if the owning thread needs new pages, performs
an allocation larger than mimalloc's medium-object limit, or the thread
exits. This means that we don't free pages if a thread's allocation
pattern quiesces or falls into a pattern that can be serviced by
existing pages. This can be problematic for threads that allocate a
bunch of memory and then settle into the previous pattern.
It's worth noting that this may increase GC pause times, though it's not clear
by how much. There are a few alternatives if folks are concerned about overhead:
page_listif over a certain size threshold.page_liston manual calls togc.collect.