RFR: 8367413: Refactor types in Arguments::set_heap_size() [v6]

[Albert Mingkun Yang]

On Wed, 8 Oct 2025 09:57:38 GMT, Joel Sikström <jsikstro at openjdk.org> wrote:

>> Hello,
>> 
>> There are several integer types used when setting the heap size ergonomically in `Arguments::set_heap_size()`, such as julong, uint64_t and size_t. It's not clear if this code works as intended on a 32-bit VM with more than 4GB physical memory. There might be issues when converting to/from size_t and uint64_t that we don't handle properly. I suggest we should be more robust and have more control over transitions between potentially smaller types. 
>> 
>> Additionally, I've gone ahead and added comments which I think makes it easier to understand what's going on in this function. I've tried my best to leave the existing behavior unchanged, apart from type conversion.
>> 
>> Testing:
>> * Oracle's tier1-8 on all Oracle supported platforms
>
> Joel Sikström has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Make limit_by_size_t_max to a static function in arguments.cpp

Marked as reviewed by ayang (Reviewer).

src/hotspot/share/runtime/arguments.cpp line 1510:

> 1508: static const size_t DefaultHeapBaseMinAddress = HeapBaseMinAddress;
> 1509: 
> 1510: static size_t limit_by_size_t_max(uint64_t value) {

I wonder if `clamp_by_size_t_max` sounds better. Up to you.

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PR Review: https://git.openjdk.org/jdk/pull/27224#pullrequestreview-3314359536
PR Review Comment: https://git.openjdk.org/jdk/pull/27224#discussion_r2413529193