RFR: 8347129: cpuset cgroups controller is required for no good reason

[Ashutosh Mehra]

On Tue, 14 Jan 2025 15:09:26 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

>> Please review this small change to make the `cpuset` cgroups controller optional as far as the JDK is concerned. The rationale is that:
>> 
>> - Some distributions now don't have it enabled by default (e.g. Fedora 41), which breaks automatic container detection logic.
>> - CPU limits enforced with `--cpuset-cpus` is reflected with the `sched_getaffinity` system call and, thus, the controller doesn't need to be mandatory. The current failure to detect the controller results in no container limits being detected with is bad.
>> 
>> The fix is rather simple. Make `cpuset` controller look-up from `/proc/cgroups` optional (like the `pids` controller) and continue. `OSContainer::active_processor_count()` still behaves as before (should there be a `cpuset` limit) as it's covered by `os::Linux::active_processor_count()` which serves as the upper bound of other container cpu limits.
>> 
>> While at it, I've also fixed the logging bug by re-arranging the `const char*` values. `cpuset` is index `0`, `cpu` is index `1`.
>> 
>> Testing:
>> - [x] GHA
>> - [x] Linux container tests in `test/hotspot/jtreg/containers` on Linux cgroups v1 and cgroups v2 as well as on an affected system (F41 on cg v2). All pass.
>> 
>> Thoughts?
>
> Thanks for the review!

@jerboaa Should this block be updated to not return false as the cpuset is now an optional subsystem.

https://github.com/openjdk/jdk/blob/56c780078f84a2571b779d90f528d5bcab2a9dfd/src/hotspot/os/linux/cgroupSubsystem_linux.cpp#L498-L503

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PR Comment: https://git.openjdk.org/jdk/pull/23037#issuecomment-2590217293