RFR: 8327097: GenShen: Align PLAB sizes down rather than up

[Kelvin Nilsen]

On Thu, 29 Feb 2024 17:25:13 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> When adjusting LAB sizes, round down rather than rounding up.  Otherwise, we may violate the ShenandoahHumongousThreshold bound.
>
> test/hotspot/jtreg/ProblemList.txt line 94:
> 
>> 92: gc/TestAllocHumongousFragment.java#static 8298781 generic-all
>> 93: gc/stress/gclocker/TestExcessGCLockerCollections.java 8229120 generic-all
>> 94: gc/shenandoah/TestHumongousThreshold.java 832700 macos-aarch64
> 
> Not sure if it matters, but the ticket number looks too short. I also think the os name is `macosx`, based on other disabled tests. If that doesn't work, I think `generic-all` would also be fine temporarily.

Good eyes.  Thank you.

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PR Review Comment: https://git.openjdk.org/shenandoah/pull/401#discussion_r1508042898