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Tuning maxvnodes for better system peformance
Authored by: bdm on Jul 19, '03 12:24:01AM

I'm also suspicious about this hint. It seems to me that unless you are doing something that requires an extremely large number of files open at once (or open repeatedly), a very large value of maxvnodes is not going to help. It can even hurt as the ram used to hold all those vnodes could be put to other use.

Brendan.



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Tuning maxvnodes for better system peformance
Authored by: mlaster on Mar 28, '04 08:20:48AM

I'm a bit suspicious of this too. I've tried it out and from everything I can tell, the number of vnodes in use will never shrink significantly. I think I only saw vnode shrinkage when I actually deleted recently touched files.
Being that is never shrinks, any system with any maxvnodes setting will eventually hit the 99% usage mark, making this a useless metric for determining that your maxvnodes amount is too low.

Also, I've been searching the web, and I still haven't found a clear definition of exactly what a vnode is cachine? Is it just filesystem metadata, or does this somehow factor into caching the file contents as well? Does a 6 gig file still take only one vnode slot when it is cached?

How do we measure the effectiveness of the unified buffer cache? Is that
what the hit_rate value is in vm_stat?

Does increasing the maxvnodes help better utilize unused RAM? I looked
at our CVS server and it is hardly using it's RAM and could maybe take advantage of this. The machine has 1.5 gig of RAM and 1.1 gig of it is still free after 18 days of uptime. I suspect that if OS X hasn't utilized it after 2 weeks, it's not likely to start using it soon. It would probably better be used for disk caching.

If sure would be nice if Apple would document the low levels of the system a bit better :-)



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