RFR: 8311648: Refactor the Arena/Chunk/ChunkPool interface [v2]

[Thomas Stuefe]

On Fri, 7 Jul 2023 13:59:06 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

>> Hi,
>> 
>> This PR refactors the Arena code without introducing any changes in behavior. I believe that this leads to a much clearer API and that this will in turn simplify the maintenance of this code. `Chunk` is now much more "dumb", mainly acting as a way of interrogating the chunk of data that it is holding. The `ChunkPool` gains a more prominent role, being entirely responsible for the memory allocation strategy used. `Arena` is basically unchanged, as it orchestrates the usage of these two APIs. The `chop` and `next_chop` methods are re-defined to be static inside of `Chunk`, having an object `delete` itself  is very surprising, so I'm happy to get rid of that.
>> 
>> I hope that you agree with me on these changes!
>> 
>> Cheers,
>> Johan
>
> Johan Sjölen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Hide ChunkPool, make ChunkPoolCleaner be started from Arena

Hi Johan,

cursory review.

Could you please give this a massage and minimize deltas a bit? Would make review and backporting easier. Seems several things moved without much reason to move. 

Thanks!

src/hotspot/share/memory/arena.cpp line 52:

> 50:   static ChunkPool _pools[_num_pools];
> 51: 
> 52:   Chunk*       _first;        // first cached Chunk; its first word points to next chunk

I'd probably leave out the comment since its pretty obvious how this works.

src/hotspot/share/memory/arena.cpp line 60:

> 58:   void return_to_pool(Chunk* chunk);
> 59:   // Prune the pool
> 60:   void prune();

Comment just repeats the name. I'd either omit it or describe what the function is doing.

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PR Review: https://git.openjdk.org/jdk/pull/14803#pullrequestreview-1520679898
PR Review Comment: https://git.openjdk.org/jdk/pull/14803#discussion_r1257199238
PR Review Comment: https://git.openjdk.org/jdk/pull/14803#discussion_r1257199011