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

[Albert Mingkun Yang]

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

src/hotspot/share/gc/g1/g1CollectionSet.cpp line 328:

> 326:     assert(_optional_old_regions.length() == 0, "must be");
> 327: 
> 328:     if (collector_state()->in_mixed_phase()) {

Why checking the same condition again (L322 the first time)?

src/hotspot/share/gc/g1/g1CollectionSet.cpp line 329:

> 327: 
> 328:     if (collector_state()->in_mixed_phase()) {
> 329:       time_remaining_ms = _policy->select_candidates_from_marking(&candidates()->marking_regions(),

`time_remaining_ms` seems unused after the assignment.

src/hotspot/share/gc/g1/g1CollectionSetCandidates.cpp line 47:

> 45: }
> 46: 
> 47: void G1CollectionCandidateList::append_unsorted(HeapRegion* r) {

Some methods in this file seem never used.

src/hotspot/share/gc/shared/ptrQueue.hpp line 43:

> 41: class BufferNode;
> 42: class PtrQueueSet;
> 43: class PtrQueue : public CHeapObj<mtGC> {

Why is this required?

(Seems to work fine without it when I tried it.)

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/13666#discussion_r1182204221
PR Review Comment: https://git.openjdk.org/jdk/pull/13666#discussion_r1182204738
PR Review Comment: https://git.openjdk.org/jdk/pull/13666#discussion_r1182212123
PR Review Comment: https://git.openjdk.org/jdk/pull/13666#discussion_r1182203296