RFR: 8331560: Refactor Hotspot container detection code so that subsystem delegates to controllers [v8]

[Johan Sjölen]

On Tue, 2 Jul 2024 08:27:50 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

>> Please review this preparatory PR which is an enabler for some bugfix/alignment work (e.g. [JDK-8322420](https://bugs.openjdk.org/browse/JDK-8322420)). The idea is to delegate limit lookup to controllers (`memory`, `cpu`, etc.) from the overarching `CgroupSubsystem` class. This way we can - once the cg type has been detected - "adjust" a controller's path to the limit files when the controller is being created (on init) and then left alone. In this case, the two preparatory entry points are `CgroupUtil::processor_count()` taking a version-agnostic `CgroupCpuController` to do the actual look-up and `CgroupMemoryController::read_memory_limit_in_bytes()` for the same in terms of memory limits.
>> 
>> This enables setting the contoller's path to the interface files (wherever it might be in the hierarchy of it's original cgroup path), look up the limit and "freeze" the path once it found a - lower - limit.
>> 
>> It also ensures that both cgroup versions return `-1` or `-2` (`OSCONTAINER_ERROR`) - in both cases negative - for some notion of unlimited. I.e. it makes the upper bound by the host's physical memory apparent in the version agnostic classes.
>> 
>> Testing:
>> - [x] GHA
>> - [x] gtest:cgroupTest tests
>> - [x] container tests on Linux cgv1 and cgv2 on x86_64
>> 
>> Thoughts?
>
> Severin Gehwolf has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix tabs => spaces

I went through it again, LGTM. Nice!

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Marked as reviewed by jsjolen (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/19085#pullrequestreview-2153845069