[Python-Dev] No longer enable Py_TRACE_REFS by default in debug build (original) (raw)

Michael Sullivan sully at msully.net
Tue Apr 16 22:05:50 EDT 2019

On Tue, Apr 16, 2019 at 2:11 AM Victor Stinner <vstinner at redhat.com> wrote:

Hi Michael,

Do you know the tracemalloc module? Did you try it? It works on a regular Python (compiled in debug mode). I would be curious to know if tracemalloc also allows you to track the memory leak. Playing around with it a little it does not seem super helpful here (unless I am missing something): it tracks the allocations based on the python call stack, which doesn't help here, in a C extension module generated from python code.

Though, in the the mypyc case, we could implement a debug option for creating dummy frames so that we always have a useful call stack. That seems like less of an option for actual hand-written extension modules, though. (Though on the flip side, the python call stacks might be more useful there.)

sys.getobjects() is just a list of objects. Do you have a tool written

on top of it to track memory leaks? If yes, how?

Not really.

We have a very simple memory profiler built on top of gc.get_objects() that just reports how many of different types of objects there are and how much memory they are using: https://github.com/python/mypy/blob/master/mypy/memprofile.py. I swapped out gc.get_objects() for sys.getobjects(), observed that we were leaking int objects, and inspected the live int objects, which gave a pretty good clue where the leak was.

Victor

Le mar. 16 avr. 2019 à 00:28, Michael Sullivan <sully at msully.net> a écrit : > > > The main question is if anyone ever used PyTRACEREFS? Does someone > > use sys.getobjects() or PYTHONDUMPREFS environment variable? > > I used sys.getobjects() today to track down a memory leak in the mypyc-compiled version of mypy. > > We were leaking memory badly but no sign of the leak was showing up in mypy's gc.getobjects() based profiler. Using a debug build and switching to sys.getobjects() showed that we were badly leaking int objects. A quick inspection of the values in question (large and random looking) suggested we were leaking hash values, and that quickly pointed me to https://github.com/mypyc/mypyc/pull/562. > > I don't have any strong feelings about whether to keep it in the "default" debug build, though. I was using a debug build that I built myself with every debug feature that seemed potentially useful. > > -sully _> ________________________ > Python-Dev mailing list > Python-Dev at python.org > https://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: https://mail.python.org/mailman/options/python-dev/vstinner%40redhat.com

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