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

[MRAB]

On 2017-03-30 19:04, INADA Naoki wrote:
> 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
>>>>
Copying a small set _might_ double its memory usage.


Python 3.5.2 (v3.5.2:4def2a2901a5, Jun 25 2016, 22:18:55) [MSC v.1900 64 
bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
 >>> import sys
 >>> s = set(range(10))
 >>> sys.getsizeof(s)
736
 >>> sys.getsizeof(set(s))
736
 >>>
 >>> sys.getsizeof(set(set(s)))
736


Python 3.6.1 (v3.6.1:69c0db5, Mar 21 2017, 18:41:36) [MSC v.1900 64 bit 
(AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
 >>> import sys
 >>> s = set(range(10))
 >>> sys.getsizeof(s)
736
 >>> sys.getsizeof(set(s))
1248
 >>>
 >>> sys.getsizeof(set(set(s)))
1248
 >>>