RFR: 8343704: Bad GC parallelism with processing Cleaner queues [v7]

[Aleksey Shipilev]

On Fri, 15 Nov 2024 07:32:37 GMT, Axel Boldt-Christmas <aboldtch at openjdk.org> wrote:

> > I have been playing with [8343704-node-cache.txt](https://github.com/user-attachments/files/17753986/8343704-node-cache.txt) -- is that what you had in mind?
> 
> Yes. It amortises the allocation over at least NODE_CAPACITY inserts, instead of 1 in the worst case.

Pushed that into PR. There is some measurable impact for dealing with this node cache during heavy churn, but it is still well within the improvements margin we get wholesale.

I am willing to accept this single-slot cache for three reasons: a) crossing the artificial border with just a single cleaner registering and unregistering looks like something we want to mitigate to avoid surprises; b) Cleaners are recommended by Javadoc to be shared, so wasting another node should not be as painful; c) the implementation and maintenance cost is not high.

But I would draw the line at this heuristics, and do nothing smarter :)

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PR Comment: https://git.openjdk.org/jdk/pull/22043#issuecomment-2478457365