[pypy-issue] Issue #2781: memory leak in pypy default branch as of 20180401 (pypy/pypy)

[pv]

New issue 2781: memory leak in pypy default branch as of 20180401
https://bitbucket.org/pypy/pypy/issues/2781/memory-leak-in-pypy-default-branch-as-of

pv:

The following seems to leak memory on current pypy default branch (045483a22d66):
```
# pypy -mensurepip
# pypy -mpip install numpy==1.14.2
# pypy runthis.py
# -> memory usage increases, without upper bound
import numpy as np
x = np.zeros([1])
while True:
    x - x
```
The memory usage seems to grow without upper bound. This does not occur on pypy-5.10.0, for which the memory usage stays constant. The issue is also visible in current py3.5 branch.