mbuf patch with sysctl suggestions too

[Mike Silbersack]

On Wed, 24 Jan 2007, Randall Stewart wrote:

> Well.. no I believe someone (was in Lin) mentioned that
> you can get a live-lock if you allow a reduction.. and
> thus the mbuf clusters were NOT allowed to be reduced..

I messed around with this a bit when changing the limit on 
net.inet.tcp.maxtcptw.  It looked to me as if lowering the limit on a 
zone, even one that has UMA_ZONE_NOFREE, worked as expected.  (As expected 
in the UMA_ZONE_NOFREE case was that the zone could not shrink below the 
maximum that was ever allocated in it.)

I can see how problems could result if someone starts changing that 
setting while the system is in some sort of mbuf exhaustion state, but I 
think that the benefit of being able to tune it most of the time far 
outweighs the disadvantage of things going wrong in a few cases.

Granted, I haven't even looked at your patch, so I could be missing 
something subtle. :)

Mike "Silby" Silbersack