Integrated: JDK-8272112: Arena code simplifications

[Thomas Stuefe]

On Sat, 7 Aug 2021 05:30:54 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> May I please have reviews for this small change. This is pure code cleanup, issues that were identified by code review when working on JDK-8270308. 
> 
> The patch results in less code (excluding the new gtest), bit easier to maintain. I have some smaller functional improvements in the pipeline and would like to get this code cleanup out of the way first.
> 
> Changes:
> 
> - Made `ChunkPool` an automatic object. We can remove `chunkpool_init()` and instead rely on automatic initialization.
> 
> - Instead of having four named pools that need to be handled individually and selected via awkward switch constructs (see the old `Chunk::operator new()` and `::operator delete()`), we replace it with an array and a static selector (`ChunkPool* get_pool_for_size(size_t size)`).
> 
> - Removed `ChunkPool::_num_used`. It was nowhere queried, and its usefulness was questionable since these numbers don't include chunks with "special" sizes. The easiest way to obtain the footprint of arena chunks is via NMT.
> 
> - Before, we had two places where the backing memory of Chunks was allocated: in `ChunkPool::allocate()` and in `Chunk::operator new()`. The former was unnecessary. I streamlined that: removed the ability to allocate from `ChunkPool::allocate()` and renamed it to `ChunkPool::remove_chunk()`. Now Chunks are only allocated in `Chunk::operator new() `and ChunkPool just serves as Chunk cache.
> 
> - Renamed `ChunkPool::free_all_but()` to `ChunkPool::prune()` and removed the argument, made it a method-local constant (it had been a constant before in the caller of that function).
> 
> - I added a new gtest to test Chunk allocation and pooling a little.
> 
> 
> Functionally, nothing should have changed with this patch, this is pure code grooming.
> 
> ----
> 
> Tests: 
> - GHA
> - I manually tested on 64-bit and 32-bit, with and without UseMallocOnly. I also manually checked that pool usage is as expected.

This pull request has now been integrated.

Changeset: d06d0b9e
Author:    Thomas Stuefe <stuefe at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/d06d0b9e9d9d27aa549455f19b9803752431bcbb
Stats:     166 lines in 3 files changed: 56 ins; 61 del; 49 mod

8272112: Arena code simplifications

Reviewed-by: kbarrett, coleenp

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PR: https://git.openjdk.java.net/jdk/pull/5040