RFR: 8254562: ZGC: Remove ZMarkRootsTask [v2]

[Stefan Karlsson]

On Mon, 12 Oct 2020 13:24:27 GMT, Erik Österlund <eosterlund at openjdk.org> wrote:

>> Stefan Karlsson has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Also remove ZRelocateRootTask and ZRootsIterator
>
> I agree with Per that we can start by removing the marking stuff first. I think Coleen is just about to move the JVMTI
> tag map oops into OopStorage, and then we can nuke the relocation code too.

Talked to Per. The plan is to revert the removal of the ZRelocateRootsTask, but at least run that code with only one
worker thread. Running tests now.

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PR: https://git.openjdk.java.net/jdk/pull/601