"Hypervisors are the modern micro kernels. Microkernel is not
about size, but about what should be in kernel mode. Linus's ideas
about filesystems are rather old. He thinks that it is a bad idea
to push the filesystems to user space, leaving the memory manager
to run in kernel mode.
"The bulk of the memory buffers are filesystem contents, and you
need both of them to work together. This is true for root
filesystems with relatively small amounts of data but not true when
it comes to scalable storage systems. Don't let the kernel manage
the memory for you. In my opinion, Kernel-space does a poor job of
handling large amounts of memory with 4k pages."