March 2012
Chapter 9, on Memory of Andries Brouwer's Some Remarks on the Linux Kernel (that title is a huge understatement), holds the steps to turn of memory overcommit:
root@server:~# echo 2 > /proc/sys/vm/overcommit_memory
root@server:~# echo 80 > /proc/sys/vm/overcommit_ratio
root@server:~# cat <<EOF >> /etc/sysctl.conf
# 0 = default, 1 = malloc always succeeds, 2 = strict overcommit
vm.overcommit_memory = 2
# commit no more virtual address space than swap + 80% of RAM
vm.overcommit_ratio = 80
EOF
Oh, and RedHat has a few useful notes on /proc/meminfo.
A few more relevant links...