RFR: 8337511: Implement JEP-404: Generational Shenandoah (Experimental) [v3]

[Roman Kennke]

On Tue, 8 Oct 2024 17:20:31 GMT, William Kemper <wkemper at openjdk.org> wrote:

>> This PR merges JEP 404, a generational mode for the Shenandoah garbage collector. The JEP can be viewed here: https://openjdk.org/jeps/404. We would like to target JDK24 with this PR.
>
> William Kemper has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 478 commits:
> 
>  - Fix merge error
>  - Merge remote-tracking branch 'jdk/master' into great-genshen-pr-redux
>  - Merge remote-tracking branch 'jdk/master' into great-genshen-pr-redux
>  - Merge branch 'shenandoah/master' into great-genshen-pr-redux
>  - Merge
>  - 8341099: GenShen: assert(HAS_FWD == _heap->has_forwarded_objects()) failed: Forwarded object status is sane
>    
>    Reviewed-by: kdnilsen
>  - 8341485: GenShen: Make evac tracker a non-product feature and confine it to generational mode
>    
>    Reviewed-by: kdnilsen, ysr
>  - Merge
>  - 8341042: GenShen: Reset mark bitmaps for unaffiliated regions when preparing for a cycle
>    
>    Reviewed-by: kdnilsen
>  - 8339616: GenShen: Introduce new state to distinguish promote-in-place phase as distinct from concurrent evacuation
>    
>    Reviewed-by: kdnilsen, shade, ysr
>  - ... and 468 more: https://git.openjdk.org/jdk/compare/b9db74a6...4db1e0e1

I looked at the remaining changes, it's mostly tests. Only some minor comments/requests on those.

test/hotspot/jtreg/gc/shenandoah/TestAllocIntArrays.java line 100:

> 98: 
> 99: /*
> 100:  * @test id=generational

You are making a test configuration and call it 'generational' but then one of the two run configurations doesn't actually run with generational mode. You probably want to separate the two?

test/hotspot/jtreg/gc/shenandoah/TestAllocIntArrays.java line 163:

> 161:         final int min = 0;
> 162:         final int max = 384 * 1024;
> 163:         // Each allocated int array is assumed to consume 16 bytes for alignment and header, plus

With the upcoming 'compact headers' it's going to be only 12 bytes. If that matters, then the actual number should perhaps be a constant? Preexisting and not relevant for this PR, though.

test/hotspot/jtreg/gc/shenandoah/oom/TestAllocLargeObj.java line 1:

> 1: /*

Why are you removing the test?

test/hotspot/jtreg/gc/shenandoah/oom/TestAllocLargerThanHeap.java line 1:

> 1: /*

And this test?

test/hotspot/jtreg/gc/shenandoah/oom/TestAllocOutOfMemory.java line 1:

> 1: /*

Or is this new test subsuming several old tests?

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

Changes requested by rkennke (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/21273#pullrequestreview-2362848068
PR Review Comment: https://git.openjdk.org/jdk/pull/21273#discussion_r1796980759
PR Review Comment: https://git.openjdk.org/jdk/pull/21273#discussion_r1796983485
PR Review Comment: https://git.openjdk.org/jdk/pull/21273#discussion_r1797098313
PR Review Comment: https://git.openjdk.org/jdk/pull/21273#discussion_r1797098581
PR Review Comment: https://git.openjdk.org/jdk/pull/21273#discussion_r1797099580