RFR: 8260941: Remove the conc_scan parameter for CardTable

[Kim Barrett]

> On Feb 10, 2021, at 4:44 AM, Albert Mingkun Yang <ayang at openjdk.java.net> wrote:
> 
> On Fri, 5 Feb 2021 09:52:25 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:
> 
>> Hi,
>> 
>>  can I have reviews for this removal of the last(?) CMS-specific code in CardTable, namely some provision to indicate that cards are being scanned concurrently in Serial/Parallel GC barrier code?
>> 
>> The change simply follows the predicate into Serial/Parallel GC code which always returns false for them and removes that code.
>> 
>> In the review for JDK-8234534 I mentioned that I split this out due to unexplainable errors; testing tier1-5 three times showed none of that any more (after updating to latest code).
>> 
>> This change has only been built on Oracle-platforms and linux-x86 via github actions (https://github.com/tschatzl/jdk/actions/runs/539993964), so I would like to kindly ask maintainers of the others to compile and report issues (32 bit ARM, PPC etc).
>> 
>> Testing: tier1-5
> 
> A side note: it seems that `G1BarrierSet` is the only subclass of `CardTableBarrierSet`. Maybe it makes sense to merge them into one.

GenCollectedHeap (i.e. SerialGC) directly instantiates CardTableBarrierSet.