[Linux-ia64] Re: PCI DAC routines for SN

   From: Jesse Barnes <jbarnes@sgi.com>
   Date: Wed, 24 Apr 2002 16:13:08 -0700
   
   So the penalty for using DAC comes down to ~.0375% for a 64k I/O, and
   the benefit is that you don't have to use 32 bit mappings (which can
   be scarce on some platforms).

No some, _your_ platform.   It is the only one with this problem.

You only need this 4GB memory for consistent memory, not
for anything else!  %99 of the kernel is going to use memory
for pages and data, not descriptors.

You can use zones and whatnot to make sure this isn't a problem at
all.