9.0-RC2 re(4) "no memory for jumbo buffers" issue

Mike Andrews mandrews at bit0.com
Sat Nov 26 21:06:04 UTC 2011

I have a Supermicro 5015A-H (Intel Atom 330) server with two Realtek 
RTL8111C-GR gigabit NICs on it.  As far as I can tell, these support 
jumbo frames up to 7422 bytes.  When running them at an MTU of 5000 on 
FreeBSD 9.0-RC2, after a week or so of update, with fairly light network 
activity, the interfaces die with "no memory for jumbo buffers" errors 
on the console.  Unloading and reloading the driver (via serial console) 
doesn't help; only rebooting seems to clear it up.

I don't have this issue with any of my em(4) based systems that are also 
using a 5000 byte MTU -- and they push considerably more traffic.

I don't really consider this a regression from FreeBSD 8.2 because 8.2 
didn't support jumbos at all on this hardware... :)

What's the best way to go about debugging this...  which sysctl's should 
I be looking at first?  I have already tried raising kern.ipc.nmbjumbo9 
to 16384 and it doesn't seem to help things... maybe prolonging it 
slightly, but not by much.  The problem is it takes a week or so to 
reproduce the problem each time...

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