Re: Recommended kernel config for a dell 8450, 8 cpu, 8GB of ram.

Mark Sergeant wrote:
> Just seeking some general information. I've got a couple of dell 8 cpu
> boxes here running FreeBSD 5.1-RELEASE and am interested in peoples
> thoughts on the best kernel configs for this type of machine. I'm
> interested in the best way of making use of 8 cpu's and also seeing the
> whole 8GB of RAM.

For more than 4G of physical RAM, your only option is to enable
the PAE support.

In terms of other configuration options, it really depends on
your intended use.  In general, the PAE support doesn't allow
the address space of the combined user and kernel to exceed 4G;
what it does is let you have more processes resident instead of
being swapped out.  You also can't really increase your kernel
memory usage over the KVA size limit, in any case, and unless
you increase the KVA from 2G to 3G (simultaneously decreasing
the UVA available to user processses), you will likely run into
the "kmem_map too small", even if you set the hard limits up.

Doing this will reduce the maximum size of user processes, which
may not be what you want, given that the reason you have more
than 4G in the box in the first place is that you are expecting
to be able to make use of it.  8-).

One thing that would be helpful (and last time I looked, it still
wasn't easily supportable) would be to change the KVA/UVA ratio,
and deuinify the kernel and process address space.  Doing this
would have implications for the pipe code and the loopback device,
but it would also let you replace uiomove() to do map flipping to
copy data in and out, and basically that would give you the full
4G UVA and full 4G KVA, instead of being limited to UVA+KVA=4G.

This is basically what the Alpha, SPARC, and PPC platforms do.

-- Terry