RFR: 8232365: Implementation for JEP 363: Remove the Concurrent Mark Sweep (CMS) Garbage Collector

[Erik Joelsson]

Hello Leo,

When removing a JVM feature from the VALID_JVM_FEATURES list, it needs 
to be added to the DEPRECATED_JVM_FEATURES list. Deprecated here means 
removed here, but configure will still accept the argument (with a 
warning).

Otherwise build changes look good.

/Erik

On 2019-10-18 02:38, David Holmes wrote:
> Hi Leo,
>
> cc'ing build-dev. I think there is a process you need to follow to 
> remove VM features from the build system. And build folk need to check 
> all build changes anyway.
>
> Thanks,
> David
>
> On 18/10/2019 6:20 pm, Leo Korinth wrote:
>> Hi,
>>
>> Here is a patch that removes the CMS GC.
>>
>> I have neither tested arm nor ppc; I hope my changes to those .ad 
>> files are correct, if someone can test those architectures, that 
>> would be great.
>>
>> Please take an extra look at 
>> CollectedHeap::check_for_non_bad_heap_word_value, it was buggy before 
>> (but never called), It is now called (and hopefully correct).
>>
>> I have tried to remove most parts of CMS. I have not made it a goal 
>> to remove all traces of CMS. I guess there are much more to cleanup, 
>> and suggestions of more to remove are welcomed. I think more 
>> complicated cleanups should be dealt with in separate enhancements.
>>
>> Not fully addressed in code, but an issue that has to be dealt with, 
>> how do I obsolete -Xconcgc and -Xnoconcgc? I believe the option 
>> should be obsoleted, though I do not know if we have any precedence 
>> obsoleting -X options.
>>
>> My patch prints:
>>
>> $ java -Xconcgc -jar Notepad.jar
>> Java HotSpot(TM) 64-Bit Server VM warning: -Xconcgc uses 
>> UseConcMarkSweepGC
>>
>> I guess that is not enough for being obsolete, compare with:
>>
>> $ java -XX:UseConcMarkSweepGC -jar Notepad.jar
>> Java HotSpot(TM) 64-Bit Server VM warning: Ignoring option 
>> UseConcMarkSweepGC; support was removed in 14.0
>>
>> Bug:
>>    https://bugs.openjdk.java.net/browse/JDK-8232365
>>
>> Webrev:
>>    http://cr.openjdk.java.net/~lkorinth/8232365/00
>>
>> Testing:
>>    tier 1-5.
>>
>> Thanks,
>> Leo