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

[Leo Korinth]

On 21/10/2019 20:08, coleen.phillimore at oracle.com wrote:
> 
> 
> On 10/18/19 4:20 AM, 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.
> 
> I can send you a list of things extra things I know about.  Thank you 
> for not addressing all of the CMS special cases with this patch.
> 
> http://cr.openjdk.java.net/~lkorinth/8232365/00/src/hotspot/share/oops/oop.inline.hpp.udiff.html 
> 
> 
> This set_klass_to_list_ptr was an especially aggregious type violation. 
> Since you've touched this, can you remove these functions with your patch:
> 
>    // For when the klass pointer is being used as a linked list "next" 
> field.
>    inline void set_klass_to_list_ptr(oop k);
>    inline oop list_ptr_from_klass();

I will remove them, Thanks!
/Leo
> 
> The runtime and oops changes look good.
> Coleen
> 
> 
> 
>>
>> 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
>