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[Python-Dev] No longer enable Py_TRACE_REFS by default in debug build


On Mon, Apr 15, 2019 at 4:06 PM Nathaniel Smith <njs at pobox.com> wrote:

> On Mon, Apr 15, 2019, 15:27 Michael Sullivan <sully at msully.net> wrote:
>
>> > 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.
>>
>
> This is mostly to satisfy my curiosity, so feel free to ignore: did you
> try using address sanitizer or valgrind?
>
> I didn't, mostly because I assume that valgrind wouldn't play well with
cpython. (I've never used address sanitizer.)

I was curious, so I went back and tried it out.
It turned out to not seem to need that much fiddling to get to work. It
slows things down a *lot* and produced 17,000 "loss records", though, so
maybe I don't have it working right. At a glance the records did not shed
any light.

I'd definitely believe that valgrind is up to the task of debugging this,
but my initial take with it shed much less light than my sys.getobjects()
approach. (Though note that my sys.getobjects() approach was slotting it
into an existing python memory profiler we had hacked up, so...)

-sully


> -n
>
>>
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