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

[Thomas Fitzsimmons]

On Wed, 2 Apr 2025 19:40:10 GMT, Thomas Fitzsimmons <fitzsim 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.
>
> Thank you for re-reviewing, @jerboaa and @ashu-mehra.  I have issued the `integrate` command.  Can one of you please sponsor the change?

> JDK 21 patch is mostly clean (minor context issue). I will do the backport next week, if @fitzsim does not take it over.

@sercher It's fine with me if @jerboaa or you do the backporting; thanks!

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PR Comment: https://git.openjdk.org/jdk/pull/23811#issuecomment-3407638104