stop UBC use by filesystems

[T. Horsnell]

Many (maybe even most) applications we run, read or
write their data in streaming mode, and there would
seem to be no advantage in passing this data through
the UBC first, since the data is not re-read within
a short time. In fact it slows the response time of
the system because the UBC consumes large amounts of
system memory if these files are large, and then
there is a (sometimes substantial) delay while
enough UBC is flushed to disk to make way for a
new application to run.

1. Is there a way to restrict the amount of
   memory consumed by the UBC?

2. Is there any way of mounting a filesystem
   such that its data doesnt pass through
   the UBC at all? 

Cheers,
Terry.