Re: [PATCH v3 0/2] Don't create Python bytecode when building the kernel

Akira Yokosawa
2025-04-24T02:07:11Z

On Wed, 23 Apr 2025 19:31:36 +0300, Andy Shevchenko wrote:
> On Wed, Apr 23, 2025 at 06:30:48PM +0900, Akira Yokosawa wrote:
>> On Tue, 22 Apr 2025 10:57:33 +0300, Andy Shevchenko wrote:
>>> On Mon, Apr 21, 2025 at 10:35:29AM -0600, Jonathan Corbet wrote:
>>>> Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com> writes:
>
> [...]
>
>>>>> Would it be possible to properly support O= and create pyc / pycache
>>>>> inside the object/output dir?
>>>>
>>>> I have to confess, I've been wondering if we should be treating the .pyc
>>>> files like we treat .o files or other intermediate products. Rather
>>>> than trying to avoid their creation entirely, perhaps we should just be
>>>> sure they end up in the right place and are properly cleaned up...?
>>>>
>>>> To answer Dmitry's question, it seems that setting PYTHONPYCACHEPREFIX
>>>> should do the trick?
>>>
>>> It's not so easy. The Python is written in a way that it thinks it will never
>>> runs object files separately from the source. Hence that variable sets only
>>> the folder per script as _home_ for the cache. It's completely unusable. They
>>> took it wrong. It still can be _painfully_ used, but it will make Makefiles
>>> uglier.
>>
>> But, PYTHONPYCACHEPREFIX can be set as an environment variable.
>>
>> For example, try:
>>
>> export PYTHONPYCACHEPREFIX="$HOME/.cache/__pycache__"
>>
>> Wouldn't it be good enough for you?
>
> Of course not. We have _many_ scripts in python in kernel and having a cache
> there for _all_ of them is simply WRONG. You never know what clashes can be
> there with two complicated enough scripts which may have same module names,
> etc.
>

Interesting...

I'm suspecting you replied without having tried the setting...

FYI, this is an excerpt from list of .pyc files under __pycache__ after
building defconfig kernel and "make htmldocs"; and running

$ find . -name *.pyc" -print" under ~/.cache/__pycache__
---------------------------------------------------------------------
./home/.../git/linux/scripts/lib/kdoc/kdoc_files.cpython-312.pyc
./home/.../git/linux/scripts/lib/kdoc/kdoc_parser.cpython-312.pyc
./home/.../git/linux/scripts/lib/kdoc/kdoc_re.cpython-312.pyc
./home/.../git/linux/scripts/lib/kdoc/kdoc_output.cpython-312.pyc
[...]
./usr/lib/python3.12/xml/__init__.cpython-312.pyc
./usr/lib/python3.12/xml/parsers/expat.cpython-312.pyc
./usr/lib/python3.12/xml/parsers/__init__.cpython-312.pyc
./usr/lib/python3.12/xml/etree/ElementPath.cpython-312.pyc
./usr/lib/python3.12/xml/etree/__init__.cpython-312.pyc
./usr/lib/python3.12/xml/etree/cElementTree.cpython-312.pyc
./usr/lib/python3.12/xml/etree/ElementTree.cpython-312.pyc
./usr/lib/python3.12/mimetypes.cpython-312.pyc
[...]
./usr/lib/python3/dist-packages/sphinx/deprecation.cpython-312.pyc
./usr/lib/python3/dist-packages/sphinx/highlighting.cpython-312.pyc
./usr/lib/python3/dist-packages/sphinx/pycode/ast.cpython-312.pyc
./usr/lib/python3/dist-packages/sphinx/pycode/__init__.cpython-312.pyc
./usr/lib/python3/dist-packages/sphinx/pycode/parser.cpython-312.pyc
./usr/lib/python3/dist-packages/sphinx/config.cpython-312.pyc
[...]
./home/.../sphinx-WIP/lib/python3.12/site-packages/sphinx/deprecation.cpython-312.pyc
./home/.../sphinx-WIP/lib/python3.12/site-packages/sphinx/highlighting.cpython-312.pyc
./home/.../sphinx-WIP/lib/python3.12/site-packages/sphinx/pycode/ast.cpython-312.pyc
./home/.../sphinx-WIP/lib/python3.12/site-packages/sphinx/pycode/__init__.cpython-312.pyc
./home/.../sphinx-WIP/lib/python3.12/site-packages/sphinx/pycode/parser.cpython-312.pyc
./home/.../sphinx-WIP/lib/python3.12/site-packages/sphinx/config.cpython-312.pyc
[...]
-------------------------------------------------------------------------

As you see, each of them are stored at a path corresponding to its original
.py file. The final part of the excerpt came from me running in-development
Sphinx in a python venv with the same PYTHONPYCACHEPREFIX setting.

I don't see any possibility of clashes as you mentioned above, quoting again:

> We have _many_ scripts in python in kernel and having a cache
> there for _all_ of them is simply WRONG. You never know what clashes can be
> there with two complicated enough scripts which may have same module names,
> etc.

Or my imagination might be too limited to see your point ...

Regards,
Akira