The initial values of sysctl_tcp_mem are sometimes greater than the 
total memory in the system (particularly on SMP systems).  This patch 
ensures that tcp_mem[2] is always <= 3/4 nr_kernel_pages.

However, I wonder if we want to set this differently than the way this 
patch does it.  Depending on how far off the memory size is from a power 
of two (exactly equal to a power of two is the worst case), and if total 
memory <128M, it can be substantially less than 3/4.

   -John