[binarycrusader]

  I don't know about what other operating systems do.
  Apparently all modern unixes overcommit address space in
  much the same way as Linux. However, i can't believe that
  FreeBSD handles this as crassly as Linux does.

Solaris does not (generally, unless you use MAP_NORESERVE w/ mmap).

In general, the Linux kernel's default OOM behaviour is undesirable for the vast majority of enterprise use cases. That's why RedHat and many other vendors used to disable it by default (unknown who still does).

Why is it bad? Simple; imagine your giant database is running with a large address space mapped. Another program decides to allocate a large amount of memory. The Linux kernel sees the tasty database target, kills it, and gives the smaller program its memory. Congratulations, your database just went poof.

There's an article that discusses the advantages/disadvantages with respect to Solaris here:

http://www.oracle.com/technetwork/server-storage/solaris10/s...

The article (while old) still applies today.