The current tcp_mem initialization gives values that are really too 
small for systems with ~256-768 MB of memory, and also for systems with 
larger page sizes (ia64).  This patch gives an alternate method of 
initialization that doesn't depend on the cache allocation functions, 
but I think should still provide a nice curve that gives a smaller 
fraction of total memory with small-memory systems, while maintaining 
the same upper bound (pressure at 1/2, max as 3/4) on larger memory systems.

   -John