RFR: 8275056: Virtualize G1CardSet containers over heap region [v2]

[Thomas Schatzl]

On Wed, 27 Oct 2021 10:09:52 GMT, Stefan Johansson <sjohanss at openjdk.org> wrote:

>> Thomas Schatzl has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   32 bit compatibility - limit region size to 32M there as before. Fix test.
>
> Looks good, just a couple of small comments.

After some discussion with @kstefanj we thought it would be best to limit the ergonomics to 32M regions (the previous maximum) since the choice of heap region size affects several other internal tuning (chunk sizing for scanning remembered sets, parallelism). Their impact has not been explored too much.

The user may still manually select larger sizes up to 512M at the moment, assuming that *if* you override the defaults, we assume that you will measure the impact appropriately. Of course, feedback by users about their choice is appreciated.

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PR: https://git.openjdk.java.net/jdk/pull/6059