`ByteBufAllocator` metrics

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| metric name | type | description
| reactor.netty.bytebuf.allocator.used.heap.memory | Gauge | The number of bytes reserved by heap buffer allocator.
See xref:observability.adoc#observability-metrics-used-heap-memory[Used Heap Memory]
| reactor.netty.bytebuf.allocator.used.direct.memory | Gauge | The number of bytes reserved by direct buffer allocator.
See xref:observability.adoc#observability-metrics-used-direct-memory[Used Direct Memory]
| reactor.netty.bytebuf.allocator.heap.arenas | Gauge | The number of heap arenas (when `PooledByteBufAllocator`).
See xref:observability.adoc#observability-metrics-heap-arenas[Heap Arenas]
| reactor.netty.bytebuf.allocator.direct.arenas | Gauge | The number of direct arenas (when `PooledByteBufAllocator`).
See xref:observability.adoc#observability-metrics-direct-arenas[Direct Arenas]
| reactor.netty.bytebuf.allocator.threadlocal.caches | Gauge | The number of thread local caches (when `PooledByteBufAllocator`).
See xref:observability.adoc#observability-metrics-thread-local-caches[Thread Local Caches]
| reactor.netty.bytebuf.allocator.small.cache.size | Gauge | The size of the small cache (when `PooledByteBufAllocator`).
See xref:observability.adoc#observability-metrics-small-cache-size[Small Cache Size]
| reactor.netty.bytebuf.allocator.normal.cache.size | Gauge | The size of the normal cache (when `PooledByteBufAllocator`).
See xref:observability.adoc#observability-metrics-normal-cache-size[Normal Cache Size]
| reactor.netty.bytebuf.allocator.chunk.size | Gauge | The chunk size for an arena (when `PooledByteBufAllocator`).
See xref:observability.adoc#observability-metrics-chunk-size[Chunk Size]
| reactor.netty.bytebuf.allocator.active.heap.memory | Gauge | The actual bytes consumed by in-use buffers allocated from heap buffer pools (when `PooledByteBufAllocator`).
See xref:observability.adoc#observability-metrics-active-heap-memory[Active Heap Memory]
| reactor.netty.bytebuf.allocator.active.direct.memory | Gauge | The actual bytes consumed by in-use buffers allocated from direct buffer pools (when `PooledByteBufAllocator`).
See xref:observability.adoc#observability-metrics-active-direct-memory[Active Direct Memory]
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