RFR: 8258576: Try to get zerobased CCS if heap is above 32 and CDS is disabled [v2]

[Martin Doerr]

On Fri, 18 Dec 2020 09:42:10 GMT, Richard Reingruber <rrich at openjdk.org> wrote:

>> Please review this small enhancement if CDS is disabled.
>> 
>> It tries to get a zerobased compressed class space if we have a not-zerobased compressed oops heap, i.e. the heap is above 32g. In this case there is a good chance to locate CCS below 32g.
>> 
>> The fix passed our CI testing: JCK and JTREG, also in Xcomp mode, SPECjvm2008, SPECjbb2015, Renaissance Suite,
>> SAP specific tests with fastdebug and release builds on all platforms
>
> Richard Reingruber has updated the pull request incrementally with one additional commit since the last revision:
> 
>   In largeHeapAbove32GTest we have a klass shift of 3 on OSX too.

It would be interesting to know why aarch64 and OSX don't use shift 0 in the new test case.
But the change looks good to me.
Thanks for improving it!

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Marked as reviewed by mdoerr (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/1815