RFR: 8343704: Bad GC parallelism with processing Cleaner queues [v10]

[Brent Christian]

On Fri, 15 Nov 2024 19:30:06 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> See the bug for more discussion and reproducer. This PR replaces the ad-hoc linked list with segmented list of arrays. Arrays are easy targets for GC. There are possible improvements here, most glaring is parallelism that is currently knee-capped by global synchronization. The synchronization scheme follows what we have in original code, and I think it is safer to continue with it right now.
>> 
>> I'll put performance data in a separate comment.
>> 
>> Additional testing:
>>  - [x] Original reproducer improves drastically
>>  - [x] New microbenchmark shows no regression on "churning" tests, which covers insertion/removal perf
>>  - [x] New microbenchmark shows improvement on Full GC times (crude, but repeatable), serves as a proxy for reproducer
>>  - [x] `java/lang/ref` tests in release 
>>  - [x] `all` tests in fastdebug
>
> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   prev is not needed

src/java.base/share/classes/jdk/internal/ref/CleanerImpl.java line 239:

> 237:         /**
> 238:          * Head node. This is the only node with variable size.
> 239:          * All nodes linked from the head are always at full capacity.

Also, "This is the only node where PhantomCleanables are added" ?

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PR Review Comment: https://git.openjdk.org/jdk/pull/22043#discussion_r1844710141