Is it safe to increase / double kern.maxvnodes under FreeBSD 6.4 i386?

[Karl Pielorz]

Hi,

We had some issues at the weekend that left one of our machines with a 
very, very large sendmail queue...

While we were trying to sort it out we noticed the machine takes over 4 
minutes to go through the queue (i.e. 'mailq').

I noticed the machine was hovering around the maxvnode limit - so I upped 
it.

The 'sweet spot' appears to be:

  sysctl -w kern.maxvnodes=250000

That cuts the time to run a mailq from over four minutes down to 12 seconds.

The machine has 2Gb of RAM, and is 'moderately' loaded (normally) - is it 
wise to leave that setting at 250,000 - or is it likely to cause other 
issues (i.e. kernel memory issues) - is there any metric I can look at / 
check to see if we can get away with leaving it that high?

The only stuff I can seem to find on the 'net mostly concerns upping it 
under amd64 as that uses a different mapping method for vnodes - I can't 
seem to find anything that covers increasing it that much (2.5 * the 
default of 100,000) under i386.

As it obviously makes a huge difference for us, I'd love to leave it in 
place - but don't want to risk anything drastic like a panic.

Thanks,

-Karl