Few days ago I've implemented vnode cache - it works and file system works faster. But now I'm working on file mappings.
I found an interesting subject due to mappings design: if you have a page aligned in memory file system - you can directly maps it's storage to address space of a process.
This will avoid extra memory loss - you don't need to copy/paste data from file system storage to memory.
For example, init.fs is a flat (but not page aligned) file system - and if we will provide a page aligned file system we can avoid memory loss.
This feature already implemented in some monolithic kernels, but I don't seen that in microkernel multiservice-based OSes.