RFR: 8365606: Container code should not be using jlong/julong [v2]

[Casper Norrbin]

On Fri, 24 Oct 2025 09:45:25 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

>> Please review this revised version of getting rid of `jlong` and `julong` in internal HotSpot code. The single remaining usage is using `os::elapsed_counter()` which I think is still ok. This refactoring is for the container detection code to (mostly) do away with negative return values.
>> 
>> It gets rid of the trifold-use of return value: 1.) error, 2) unlimited values 3) actual numbers/values/limits. Instead, all container related values are now being read from the interface files as `uint64_t` and afterwards interpreted in the way that make sense for the API implementations. For example, `cpu` values will essentially be treated as `int`s as before, potentially returning a negative value `-1` for unlimited. For memory sizes the type `physical_memory_size_type` has been chosen. When there is no limit for a specific memory size a value `value_unlimited` is being returned.
>> 
>> All error cases have been changed to returning `false` in the API functions (and no value is being set in the passed in reference for the value). The effect of this is that all container related functions now return a `bool` and require a reference to be passed in for the `value` that is being asked for.
>> 
>> All usages of the API have been changed to use the revised API. There is no more usages for `OSCONTAINER_ERROR` (`-2) in HotSpot code.
>> 
>> While working on this, I've noticed that there are still some calls deep in the cgroup subsystem code to query "machine" info (e.g. `os::Linux::active_processor_count()`). I've filed [JDK-8369503](https://bugs.openjdk.org/browse/JDK-8369503) to get this cleaned-up as this patch was already getting large.
>> 
>> Testing (looking good):
>> - [x] GHA
>> - [x] All container tests (including problem listed ones) on Linux x86_64 with cg v1 and cg v2. See [this comment](https://github.com/openjdk/jdk/pull/27743#issuecomment-3390060127) below.
>> - [x] Some ad-hoc manual testing in containers using JFR (`jdk.SwapSpace` event) and `VM.info` diagnostic command.
>> 
>> Thoughts? Opinions?
>
> Severin Gehwolf has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:
> 
>  - Merge branch 'master' into jdk-8365606-jlong-julong-refactor
>  - Fix print_container_info output
>  - whitespace clean-ups and other small fixes
>  - Fix log format in container macro and scanf format
>  - Fix duplicate include in osContainer_linux
>  - 8365606: Container code should not be using jlong/julong

I'm currently looking at this, just as a quick FYI.

I'm fine with the proposed interface as it is (boolean return + passed reference). Since the adjacent `os` functions recently changed to use this interface, and the disproportionate (to me) amount of bikeshedding it took to reach a consensus on that, introducing yet another interface here, for what's essentially a subcomponent, doesn't make much sense. It's clearer if the whole `os` stack sticks to the same interface.

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PR Comment: https://git.openjdk.org/jdk/pull/27743#issuecomment-3442470839