My layman's understanding: under Linux the ARC is not integrated into the usual Linux caches which are unified and which the kernel understands. So basically t

My layman's understanding: under Linux the ARC is not integrated into the usual Linux caches which are unified and which the kernel understands. So basically the ZFS ARC is a separate chunk of RAM, which can grow and grow (thus you need to limit it) and it won't be evicted as perfectly as the kernel would evict stuff cached on xfs or ext4 filesystem.