RFR: 8329529: Serial: Move _saved_mark_word out of ContiguousSpace [v2]

[Ivan Walulya]

On Thu, 4 Apr 2024 06:51:39 GMT, Guoxiong Li <gli at openjdk.org> wrote:

>> Hi all,
>> 
>> This patch removes the field `ContiguousSpace::_saved_mark_word` and its related methods, adds the corresponding fields to `DefNewGeneration` and `TenuredGeneration`, and moves the method `ContiguousSpace::oop_since_save_marks_iterate` to `Generation`. Many usages are adjusted as well.
>> 
>> An alternative way is add a class which extends the `ContiguousSpace` to place `_saved_mark_word` and its related methods. But this way would increase the class hierarchy. Not really know whether it deserves to do that.
>> 
>> The tests `make test-tier1_gc` passed locally. Thanks for taking the time to 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 four additional commits since the last revision:
> 
>  - Remove saved mark word of eden-space and from-space.
>  - Merge branch 'master' into SAVED_MARK_WORD
>  - Set saved mark word out of oop iteration.
>  - JDK-8329529

LGTM!

Minor:

src/hotspot/share/gc/serial/defNewGeneration.hpp line 174:

> 172:   ContiguousSpace* to()   const           { return _to_space;   }
> 173: 
> 174:   // Access saved mark word

comment doesn't seem to add any value

src/hotspot/share/gc/serial/tenuredGeneration.hpp line 69:

> 67: 
> 68:   TenuredSpace*       _the_space;       // Actual space holding objects
> 69:   HeapWord*           _saved_mark_word; // Saved mark word

`// Saved mark word` seems unnecessary

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Marked as reviewed by iwalulya (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/18603#pullrequestreview-1982517478
PR Review Comment: https://git.openjdk.org/jdk/pull/18603#discussion_r1553295925
PR Review Comment: https://git.openjdk.org/jdk/pull/18603#discussion_r1553293171