On the machine which has troubles, the bug occured within about 10 days
During these days, the amount of dirty pages increased, up to 400MB.
I have testet kernel 2.6.19, 2.6.20, 2.6.22.1 and 2.6.22.10 (with our config),
and even linux-2.6.20 from ubuntu-sever. They have all shown that behaviour.
10 days ago, i installed kernel 2.6.18.5 on this machine (with backported
3ware controller code). I'm quite sure that this kernel will now fixes our
severe stability problems on this production machine (currently:
Dirty: 472 kB, nr_dirty 118).
If so, it's the "lastest" kernel i found usable, after half of a year of pain.