On Tue, Apr 16, 2019 at 2:11 AM Victor Stinner <vstinner@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.

Le mar. 16 avr. 2019 à 00:28, Michael Sullivan <sully@msully.net> a écrit :
> > The main question is if anyone ever used Py_TRACE_REFS? 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.get_objects() 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
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Night gathers, and now my watch begins. It shall not end until my death.