system slowdown - vnode related

[Marc G. Fournier]

On Mon, 26 May 2003, Mike Harding wrote:

> Er - are any changes made to RELENG_4_8 that aren't made to RELENG_4?  I
> thought it was the other way around - that 4_8 only got _some_ of the
> changes to RELENG_4...

Ack, my fault ... sorry, wasn't thinking :(  RELENG_4 is correct ... I
should have confirmed my settings before blathering on ...

One of the scripts I used extensively while debugging this ... a quite
simple one .. was:

#!/bin/tcsh
while ( 1 )
  echo `sysctl debug.numvnodes` - `sysctl debug.freevnodes` - `sysctl debug.vnlru_nowhere` - `ps auxl | grep vnlru | grep -v grep | awk '{print $20}'`
  sleep 10
end

which outputs this:

debug.numvnodes: 463421 - debug.freevnodes: 220349 - debug.vnlru_nowhere: 3 - vlruwt

I have my maxvnodes set to 512k right now ... now, when the server "hung",
the output would look something like (this would be with 'default' vnodes):

debug.numvnodes: 199252 - debug.freevnodes: 23 - debug.vnlru_nowhere: 12 - vlrup

with the critical bit being the vlruwt -> vlrup change ...

with unionfs, you are using two vnodes per file, instead of one in
non-union mode, which is why I went to 512k vs the default of ~256k vnodes
... it doesn't *fix* the problem, it only reduces its occurance ...