RFR: 8346916: [REDO] align_up has potential overflow [v3]

[Albert Mingkun Yang]

On Mon, 3 Mar 2025 09:49:25 GMT, Casper Norrbin <cnorrbin at openjdk.org> wrote:

>> src/hotspot/share/gc/parallel/psOldGen.cpp line 193:
>> 
>>> 191: #endif
>>> 192:   const size_t alignment = virtual_space()->alignment();
>>> 193:   size_t aligned_bytes  = align_up_or_min(bytes, alignment);
>> 
>> How about using `bytes = MIN2(bytes, virtual_space()->uncommitted_size())` to dodge the potential overflow? I find it more intuitive to provide a proper arg to `align_up` and expect the result to be >= arg.
>
> Changed it to this now

Thank you; my suggestion was insufficient... Need to have an early-return when `uncommitted_size` is 0 at the beginning of `PSOldGen::expand`. After this, I wonder if `align_up_or_min` is truly warranted.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23711#discussion_r1977551923