I'm using an I7 3930K (six core) CPU over-clocked at 4.5Ghz with 64Gb RAM (as my primary machine) and 3DS Max 2015 SP2 and Forest Pack Pro 4.3.6, rendering with Mental Ray; but I seem to suffer from memory leaks, including on other computers used in my small render farm when scattering a very large number of objects with Forest Pack.
For example, on my primary machine, after rendering around 30 frames, memory use progresses from about 14Gb to anywhere from 30Gb to 54Gb, and render times for a similar frame can jump from 20 minutes to 4 hours plus. Some render nodes run over 24 hours without completing a frame before I reset it--and all is well for awhile.
I ran the exact same scene / animation sequence (other than low resolution, low quality settings [including 10x10 resolution]) without any forest pack scattering, for 100 frames and memory held steady at 13.1Gb, and render time held steady and render times held steady at 1 second per frame. With all the Forest Pack Pro objects in the scene, (with the previous stated settings) the memory started at around 14.1Gb and slowly rose to 20Gb in 30 frames (before I ended the test)--render time started at 30 seconds and progressed to 47 seconds in those thirty frames. (By the way, I restarted 3ds max between each test to reset memory used).
I also ran the test with just my largest scatter group [Forest] deleted. I ran all 100 frames with memory only increasing slightly by about 1Gb and render times stayed somewhat steady from 10 seconds to 11 seconds. My largest scatter area [Forest] has approximately 52,000 Render Items at it's highest point in the animation sequence, with a Far Clipping plane camera limit of 440000" (appoximately 11km).
My second largest area [Grass] has a maximum of 18,000 Render Items in any given frame, and covers an area that is approximately 44m in radius. I have about six other groups that have less than 1,500 rendered items.
Not sure if any of the above information is useful, but if anyone has an idea about what I might be doing wrong, it would be greatly appreciated as I'm trying to keep my render times to the absolute minimum.