RFR: 8271951: Consolidate preserved marks overflow stack in SerialGC

[Thomas Schatzl]

On Thu, 5 Aug 2021 14:29:09 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

> In SerialGC we put preserved marks in space that we may have in the young gen, and failing that, we push it to an overflow stack. The overflow stack is actually two stacks, and replicate behavior of the in-place preserved marks. These can be consolidated.
> 
> Testing:
>  - [x] tier1
>  - [ ] tier2
>  - [x] hotspot_gc

Lgtm.

Pre-existing, and just a side note and not directly aimed at you: when looking at the change, there is the `PreservedMark` class in Serial GC, and `PreservedMarks` with its `OopAndMarkWord` inner class and `PreservedMarksSet` in `shared/preservedMarks.hpp` which is not perfect naming. I'll probably file an RFE to look into this.

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Marked as reviewed by tschatzl (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/5022