Kernel panic, Trap 12, page fault while in kernel mode and freeing free frag on 7.0 p5 amd64

[Laszlo Nagy]

We have a production server which keeps crashing.

Hardware: two Quad Core Xeons (5420), 8GB ECC ram, Intel S5000 
motherboard, Areca 1680-ix12 RAID card.

The memory have been replaced three times. Memtest runs OK. The 
motherboard was replaced, all firmwares updated to the latest version 
(last time an Intel engineer did this for us.)

Machine is running postgresql, postfix, apache, mod_php, dovecot.

Kernel was compiled with debug symbols. Machine configuration can be 
found here:

http://195.228.74.135/info

Core dumps are here (not all of them):

http://195.228.74.135/crash

In most cases, the error message is "page fault" but there is also a 
"freeing free frag". When there is no big load (weekends) then it runs 
for two or three days. It crashes only when there is bigger load on the 
server. On very busy days, it can crash three times a day.

I have installed exactly the same software on a desktop computer with 
amd X2 BE2350 processor and 3GB non-ecc RAM, and it ran for 6 days 
without crashing. (Unfortunately, I cannot use that computer in 
production because it is incredibly slow...)

I have found some other posts about a similar problem, but that issue 
was closed. Unfortunately, I'm not familiar with kernel debugging. Is 
this the right place to ask for help?

Thanks,

   Laszlo