Help, Mental ray for Maya chewing up 8 gig of ram

Hi all,
        Have a large scene of a house of about 3 mil pollys, has been working
till now, and only using about 3.5 to 4 gig of ram, looks like it trying to
render now, but its chewing up nearly 8-10 gig of ram and the processer usage is
going up and down like a yo yo, Cut 100 meg off the scene, now 130 meg, still no
joy, rendering with command or thu maya, chews up 8 to 10 gig plus, and with
verbosity on 5 it doesn't seem to be doing anything other than photons's going
up very slowly, ram going up fast and then clearing the cache. 40 minutes in and
it still hadn't written the 1k holding file it normally does before rendering.
Was not doing this yesterday, was running f