Subject: Re: max value of NMBCLUSTERS?
To: Emre Yildirim <emre.yildirim@US.ARMY.MIL>
From: Jason R Thorpe <>
List: netbsd-users
Date: 02/15/2001 14:17:17
On Thu, Feb 15, 2001 at 04:09:29PM -0600, Emre Yildirim wrote:

 > What's the max value of NMBCLUSTERS?  I am thinking of deploying NetBSD as a 
 > firewall that will handle lots of connections.  According to the man page and 
 > FAQ, 1024 seems to be a good value, although I remember in OpenBSD I could 
 > set it as high as 8192.  Is that possible in NetBSD?  Thanks in advance.

NMBCLUSTERS is, of course, merely an upper-bound.  But, on platforms like
the i386, which have to use a special VM map to map mbuf clusters, the
entire space required to map all mbuf clusters is reserved at boot time.

That, therefore, can limit the size of NMBCLUSTERS.  On 1.5 and later,
however, the kernel has 1G of VM space, so a large NMBCLUSTERS shouldn't
be a problem.

You can get an idea on current mbuf cluster usage by using vmstat -m and
looking at the "mclpl" pool stats.

        -- Jason R. Thorpe <>