RFR: 8270100: Fix some inaccurate GC logging

[Volker Simonis]

On Tue, 13 Jul 2021 09:40:07 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> @albertnetymk  your latest proposal is still changing the current semantics. Before, the shrink factor was reset on every invocation of `CardGeneration::compute_new_size()`. With your proposal, it will only be reset if we expand the heap.
>> 
>> My patch is really just a trivial fix of some logging errors. I'm not against changing or improving it, but before I introduce any behavioral changes, I'd like to hear a second opinion.
>
>> Before, the shrink factor was reset on every invocation of CardGeneration::compute_new_size(). With your proposal, it will only be reset if we expand the heap.
> 
> Indeed, my suggestion is flawed.
> 
>> "decaying" the shrink factor on every CardGeneration::compute_new_size() call makes sense.
> 
> Agree.
> 
>> so I would probably just set current_shrink_factor and _shrink_factor to 100 at the top of CardGeneration::compute_new_size if ShrinkHeapInSteps is false
> 
> Sounds good to me.
> 
> Re `NewSizeThreadIncrease`, what's the motivation for having it (used only by Serial) in the first place? Going through the git-log, I can only find the overflow-fix from JDK-8144527.

Thanks for the reviews @albertnetymk, @tschatzl!

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PR: https://git.openjdk.java.net/jdk/pull/4727