oom_killer

Is there anyone that could help me understand why all of a sudden with
no noticeable change in data, no change in hardware, no change in OS,
I'm seeing postmaster getting killed by oom_killer?

The dmesg shows that swap has not been touched free and total are the
same, so this system is not running out of total memory per say.

I keep thinking it's something to do with lowmem vs highmem 32bit vs
64 bit, but again no changes and I'm getting hit nightly on 2
different servers (running slon, so switched over and same thing, even
disabled memory over commit and still got nailed.

Is there anyone familiar with this or could take a look at the dmesg
output (off list) and decipher it for me?

this is a Fedora 12 system, 2.6.32.23-170. I've been reading and
appears this is yet another fedora bug, but so far I have not found
any concrete evidence on how to fix it.

Fedora 12
32gig memory, 8 proc
postgres 8.4.4, slony 1.20
5 gigs of swap (never hit it!)

Thanks
Tory