Cyclic GC threshold may need tweaks

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-08-02.12:22:29.755>
labels = ['interpreter-core', 'type-feature', '3.7']
title = 'Cyclic GC threshold may need tweaks'
updated_at = <Date 2017-08-03.12:20:42.709>
user = 'https://github.com/arigo'

bugs.python.org fields:

activity = <Date 2017-08-03.12:20:42.709>
actor = 'pitrou'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2017-08-02.12:22:29.755>
creator = 'arigo'
dependencies = []
files = []
hgrepos = []
issue_num = 31105
keywords = []
message_count = 4.0
messages = ['299656', '299698', '299700', '299702']
nosy_count = 3.0
nosy_names = ['arigo', 'pitrou', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue31105'
versions = ['Python 3.7']