RFR: Enforce max regions [v3]

[Kelvin Nilsen]

On Wed, 7 Dec 2022 22:11:42 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

>> src/hotspot/share/gc/shenandoah/shenandoahFullGC.cpp line 198:
>> 
>>> 196: 
>>> 197:   if (heap->mode()->is_generational()) {
>>> 198:     // Since we probably have not yet reclaimed the most recently selected collection set, we have to defer
>> 
>> I'd make the comment less tentative, and state:
>> 
>> // Since the most recently selected collection set may not have been reclaimed at this stage,
>> // we'll defer unadjust_avaliable() until after the full gc is completed.
>> 
>> Question: is the adjusted available value (modulo the loaned size) used by full gc for any purpose, or is it to satisfy assertion checks / verification in some of the methods invoked during full gc work below?
>
> It's not used by full GC, but the Shenandoah verifier which runs at the start of full gc and then again at the end of full gc enforces compliance with the adjusted budgets.
> 
> The verifier didn't used to care.  But I made it care with this commit, and then I had to change where we do the unadjusting...

I'll fix the comment.

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PR: https://git.openjdk.org/shenandoah/pull/179