Built-in support for a memory consumption ulimit?

After giving somebody advice, for the Nth time, to install a
memory-consumption ulimit instead of leaving his database to the tender
mercies of the Linux OOM killer, it occurred to me to wonder why we don't
provide a built-in feature for that, comparable to the "ulimit -c max"
option that already exists in pg_ctl.  A reasonably low-overhead way
to do that would be to define it as something a backend process sets
once at startup, if told to by a GUC.  The GUC could possibly be
PGC_BACKEND level though I'm not sure if we want unprivileged users
messing with it.

Thoughts?
        regards, tom lane