A bunch of people stuck around and tried, they really did and I applaud
them for it but the damage was done.  I was gone by the time ZFS came out
so I have no idea how that passed through the formal vetting process that
Sun had in place.  When I was there, if I had proposed a file system that
wouldn't use the page cache, you'd have to copy from the buffer cache
into the page cache to get mmap to work, I would have been kicked out
of the room and probably kicked out of the kernel group.  We had spent
SO FRIGGING MUCH TIME getting rid of the buffer cache, precisely because
trying to maintain coherency between the page cache (mmap) and the buffer
cache (read/write), it was clear that you wanted a unified model.