Allow to build Python without freelists

[tiran]

BPO	45522
Nosy	@vstinner, @tiran, @markshannon, @miss-islington
PRs	bpo-45522: Allow to disable freelists on build time #29056 bpo-45522: Allow to disable freelists on build time #29086

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/tiran'
closed_at = None
created_at = <Date 2021-10-19.11:06:04.660>
labels = ['expert-C-API', 'type-feature', '3.11']
title = 'Allow to build Python without freelists'
updated_at = <Date 2022-01-17.13:14:15.976>
user = 'https://github.com/tiran'

bugs.python.org fields:

activity = <Date 2022-01-17.13:14:15.976>
actor = 'vstinner'
assignee = 'christian.heimes'
closed = False
closed_date = None
closer = None
components = ['C API']
creation = <Date 2021-10-19.11:06:04.660>
creator = 'christian.heimes'
dependencies = []
files = []
hgrepos = []
issue_num = 45522
keywords = ['patch']
message_count = 6.0
messages = ['404289', '404599', '405207', '405293', '410614', '410778']
nosy_count = 4.0
nosy_names = ['vstinner', 'christian.heimes', 'Mark.Shannon', 'miss-islington']
pr_nums = ['29056', '29086']
priority = 'normal'
resolution = None
stage = 'resolved'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue45522'
versions = ['Python 3.11']

[tiran]

Freelists are an optimization trick to avoid allocation and deallocation of commonly used structures. Currently Python has freelists for frame, tuple, float, list, dict, async generators, and context objects. Small ints are also cached.

For experimentation with alternative memory allocators such as mimalloc, I would like to introduce a way to disable freelists. Tuples's _Py_tuple_state struct has a conditional check on #if PyTuple_MAXSAVESIZE > 0. I propose to add same logic to all other structs.

[miss-islington]

New changeset 9942f42 by Christian Heimes in branch 'main':
bpo-45522: Allow to disable freelists on build time (GH-29056)
9942f42

[markshannon]

I think we should revert this. It just makes working with freelists more cumbersome. Having more configure options just makes it more likely that we will fail to test some configuration.

If you want to disable freelists in your experiments, feel free to do so, but it doesn't need to be in main, IMO.

[tiran]

Which part of the patch is causing you extra work? Would you be fine if I only remove the configure option and leave the fixes for zero-length freelists (#define PyList_MAXFREELIST 0) in?

[vstinner]

Freelists for object structs can now be disabled. A new configure option --without-freelists can be used to disable all freelists except empty tuple singleton. (Contributed by Christian Heimes in bpo-45522)

Can you please document the new configuration option in https://docs.python.org/dev/using/configure.html ?

When you write :option:`--without-freelists` in what's new in Python 3.11 to get a link ;-)