RFR: 8272147: Consolidate preserved marks handling with other STW collectors [v2]

[Albert Mingkun Yang]

On Tue, 6 Jun 2023 17:02:32 GMT, Guoxiong Li <gli at openjdk.org> wrote:

>> Hi all,
>> 
>> This patch removes the class `markSweep.hpp::PreservedMark` and uses the shared `PreservedMarksSet` instead.
>> 
>> In order to keep the meaning of the field `_preserved_marks` in `markSweep`,
>> I need to use `OopAndMarkWord` explicitly. So I move `OopAndMarkWord` out of `PreservedMarks`.
>> 
>> Tests:
>> `hotspot:tier1` passed locally (x86 & linux).
>> 
>> Thanks for the review.
>> 
>> Best Regards,
>> -- Guoxiong
>
> Guoxiong Li has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:
> 
>  - Use the method 'adjust_during_full_gc' and polish the included header.
>  - Merge branch 'master' into JDK-8272147
>  - JDK-8272147

src/hotspot/share/gc/serial/markSweep.cpp line 156:

> 154:     _preserved_marks[_preserved_count++] = OopAndMarkWord(obj, mark);
> 155:   } else {
> 156:     _preserved_overflow_stack_set.get()->push_if_necessary(obj, mark);

Why not `push_always`? I'd expect this mark must be preserved.

src/hotspot/share/gc/serial/markSweep.cpp line 200:

> 198:   // adjust the oops we saved earlier
> 199:   for (size_t i = 0; i < _preserved_count; i++) {
> 200:     MarkSweep::adjust_pointer(_preserved_marks[i].get_oop_pointer());

There are still some unnecessary null-checks.

I wonder if one can add new API in `PreservedMarks` to adjust oops.


void adjust_preserved_mark(OopAndMarkWord* elem) {
  oop obj = elem->get_oop();
  if (obj->is_forwarded()) {
    elem->set_oop(obj->forwardee());
  }
}


Then `_preserved_marks[]` serves just as a buffer to the overflow array  -- how their contents are processed is decided at one place and outside Serial.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14274#discussion_r1221407347
PR Review Comment: https://git.openjdk.org/jdk/pull/14274#discussion_r1221410875