NOTE
Netty PooledByteBufAllocator
Pooled ByteBuf allocation, arenas/chunks/suballocation concepts, reuse benefits, and version-sensitive allocator internals.
This is a historical learning note and may contain outdated or incomplete understanding.
PooledByteBufAllocator reuses memory rather than requesting/releasing fresh backing storage for every buffer. Netty versions organize pooled memory through arena/chunk/page/subpage-style structures and caches to reduce allocation overhead/fragmentation.
Exact size classes and internal data structures have changed over time; they are not application contracts.
Operationally, pooled direct memory remains process/native memory and can be retained by pools/caches even after a logical buffer is released for reuse. Monitor allocator/native memory separately from Java heap.