Program uses twice as much memory in Python 3.6 than in Python 3.5

INADA Naoki songofacandy at gmail.com
Thu Mar 30 14:04:15 EDT 2017


Maybe, this commit make this regression.

https://github.com/python/cpython/commit/4897300276d870f99459c82b937f0ac22450f0b6

Old:
minused = (so->used + other->used)*2  (L619)

New:
minused = so->used + other->used  (L620)
minused = (minused > 50000) ? minused * 2 : minused * 4;  (L293)

So size of small set is doubled.

$ /usr/bin/python3
Python 3.5.2+ (default, Sep 22 2016, 12:18:14)
[GCC 6.2.0 20160927] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> s = set(range(10))
>>> sys.getsizeof(frozenset(s))
736
>>>

$ python3
Python 3.6.0 (default, Dec 30 2016, 20:49:54)
[GCC 6.2.0 20161005] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import  sys
>>> s = set(range(10))
>>> sys.getsizeof(frozenset(s))
1248
>>>



On Fri, Mar 31, 2017 at 2:34 AM, INADA Naoki <songofacandy at gmail.com> wrote:
> I reproduced the issue.
> This is very usual, memory usage issue.  Slashing is just a result of
> large memory usage.
>
> After 1st pass of optimization, RAM usage is 20GB+ on Python 3.5 and
> 30GB on Python 3.6.
> And Python 3.6 starts slashing in 2nd optimization pass.
>
> I enabled tracemalloc while 1st pass.  Results is end of this mail.
> It seems frozenset() cause regression, but I'm not sure yet.
> I don't know what is contents of frozenset yet.  (I know almost
> nothing about this application).
>
> Jan, do you know about what this is?
> Could you make script which just runs `transitive_closure(edges)` with
> edges similar to
> `log_reduction.py spaun`?
>
> I'll dig into it later, maybe next week.
>
> ---
> Python 3.6.1
> 1191896 memory blocks: 22086104.2 KiB
>   File "/home/inada-n/work/gosmann-frontiers2017/gosmann_frontiers2017/optimized/optimizer.py",
> line 85
>     reachables[vertex] = frozenset(reachables[vertex])
>   File "/home/inada-n/work/gosmann-frontiers2017/gosmann_frontiers2017/optimized/optimizer.py",
> line 410
>     self.dependents = transitive_closure(self.dg.forward)
> 602986 memory blocks: 51819.1 KiB
>   File "<string>", line 14
>   File "/home/inada-n/work/gosmann-frontiers2017/gosmann_frontiers2017/optimized/optimizer.py",
> line 634
>     first_view=None, v_offset=0, v_size=0, v_base=None)
>
> Python 3.5.3
> 1166804 memory blocks: 11116407.0 KiB
>   File "/home/inada-n/work/gosmann-frontiers2017/gosmann_frontiers2017/optimized/optimizer.py",
> line 85
>     reachables[vertex] = frozenset(reachables[vertex])
>   File "/home/inada-n/work/gosmann-frontiers2017/gosmann_frontiers2017/optimized/optimizer.py",
> line 410
>     self.dependents = transitive_closure(self.dg.forward)
> 602989 memory blocks: 51819.3 KiB
>   File "<string>", line 14
>   File "/home/inada-n/work/gosmann-frontiers2017/gosmann_frontiers2017/optimized/optimizer.py",
> line 634
>     first_view=None, v_offset=0, v_size=0, v_base=None)


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