Re: [9fans] 9P optimization

["ron minnich" <rminnich@gmail.com>]

I wrote (a long time ago) a caching file system, for root file
systems, described here:
http://mbgokhale.org/rminnich/job/autocacher/autocache.ps, that did
the simple thing: once you have the file, don't bother checking with
the server until time + DeltaT, This might not work well for you, but
in 1989, it worked wonderfully well as a root file system because:
1. most files in most root file systems are never even looked at
(particularly man pages!)
2. They don't change much anyway -- think about it -- how often do
people like to upgrade :-)

So it is not always the case that you need to stat the cached files on
each access. In fact, we watched NFS traffic on our backbone at the
SRC for several months, and, as many other people have found, most
files are mostly read.

This type of optimization is fairly trivial for CFS, and would end up
covering most files (see above); the few read-write ones left would
not really hurt you too much. You could do much better in 9p because
it is stateful.

I have a new implementation of the autocacher (it's only for NFS)
which I wrote ca. 1999, before I got to LANL; I had lost it but found
it on my last day of work at LANL. I'll try to get it on my web page.
It's a very simple program.

thanks

ron