RFR: 8349988: Change cgroup version detection logic to not depend on /proc/cgroups [v4]

[Severin Gehwolf]

On Thu, 8 May 2025 08:32:01 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

>>> @jerboaa @fitzsim Does the current mainline code handles mixed configuration where in some controllers are v1 and others v2? For example cpu controller is mounted as v1 while memory controller as v2. If yes, does this patch continue to support such configuration?
>> 
>> The current code does not allow mixed configuration for "relevant" controllers (essentially cpu and memory). That is, they ought to be v1 or v2. In the hybrid case (systemd running on unified), it's considered v1. I don't think this patch changes any of it.
>
>> @jerboaa @fitzsim, is there any plan to backport this fix (to 21)?
> 
> Eventually yes. But this change hasn't seen a lot of real-world exposure yet. It would be good to have that before attempting a backport.

> Hi @jerboaa,
> We are recieving multiple customer reports on the issue with 6.14 HWE kernels.
> I would like to backport this to 21.0.10 & 17.0.18. Do you think it could be safe for the upcoming January update release?

I tend to agree. Note that it's an issue on *how* the actual kernel is configured. But Ubuntu 24.04 LTS is affected. Noted as such in the bug recently: https://bugs.openjdk.org/browse/JDK-8349988

First step would be JDK 21. JDK 17 I'm not sure. It'll depend how the patch will look like.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/23811#issuecomment-3400771974