I started a thread on the python-dev mailing list:
https://mail.python.org/archives/list/python-dev@python.org/thread/YEY2TZIWC6HGMM5Y3QKWKMEBT5Y5C324/

Serhiy:
> I used COUNT_ALLOCS for curiosity. But I needed slightly different information, so in any case I patched the code.

Did you use it recently? I understand that the unmodified feature didn't help for your use case. Was it to debug memory leaks?


Serhiy:
> AFAIK COUNT_ALLOCS is used in some large projects (maybe Fedora). It was already discussed somewhere on the tracker, but I have no a link.

Did you read previous comments, especially msg360985? It's no longer used in Fedora :-) Technically, it's still used in the python2 package, but it's gone from python3 package. But this issue is about Python 3.9, not Python 2 ;-)

FYI I'm now working in the Python Maintenance team at Red Hat which maintains python2 and python3 packages of Fedora.

By the way, Charalampos Stratakis is also in my team and he replied on python-dev:

"I've never used this feature and it was quite the hassle to maintain those patches downstream, so in my biased opinion, I would welcome the removal."

https://mail.python.org/archives/list/python-dev@python.org/message/4BI64IXNZMJGXNHOA34UJ35V74IGJNZF/