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

[Per Liden]

Hi Erik,

On 10/18/19 2:54 PM, Erik Joelsson wrote:
> 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).

Are we really treating the list of JVM feature as a public/stable API, 
or is there some other reason for this? Would the plan be to remove it 
from the DEPRECATED_JVM_FEATURES in JDK 15?

cheers,
Per

> 
> 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