RFR: 8306541: Refactor collection set candidate handling to prepare for JDK-8140326

[Thomas Schatzl]

On Wed, 26 Apr 2023 09:20:46 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

> Hi all,
> 
>   please review this refactoring of collection set candidate set handling.
> 
> The idea is to improve the interface to collection set candidates and prepare for having collection set candidates available at any time to evacuate them at any young collection.
> 
> These preparations to allow for multiple sources for these candidates (from the marking, as now, and from retained regions, i.e. evacuation failed regions as per [JDK-8140326](https://bugs.openjdk.org/browse/JDK-8140326)).
> 
> This patch only uses candidates from marking at this time.
>  
> Also moves gc efficiency out of HeapRegion and associate it to the list element as it's not used otherwise.
>     
> In detail:
>     * the collection set candidates set is not temporarily allocated any more, but the candidate collection set object is available all the time.
>     
>     * G1CollectionSetCandidates is the main class, representing the current candidates. Contains the "from marking" candidate list only (at this point).
>     
>     * there are several additional helper sets/lists
>       * G1CollectionSetRegionList: list of HeapRegion*, typically sorted by efficiency (but not necessarily). Also does not contain gc efficiences.
>       * G1CollectionCandidateList: list of candidates, i.e. HeapRegion* with their gc efficiency. Building block for the actual collection set candidates list.
>     
> All these sets implement C++ iterators for simpler use in various places.
>     
> Testing:
>  - this patch only: tier1-3, gha
>  - with JDK-8140326 tier1-7 (or 8?)
> 
> Thanks,
>   Thomas

The first two commits in the branch https://github.com/openjdk/jdk/compare/master...tschatzl:jdk:remove-pinned-mask show this change (first two patches) in context of what is to come for [JDK-8140326](https://bugs.openjdk.org/browse/JDK-8140326)), which is the fourth patch.

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PR Comment: https://git.openjdk.org/jdk/pull/13666#issuecomment-1523085024