The .blend files of Orange are requiring more and more memory to render/composite and Ton has been struggling to find a solution. As it turns out, OSX (Orange uses an Apple XServe renderfarm) can only allocate 1.5GB per application at a time and windows seem to have similar problems.
He was able to come up with a solution though and it looks like it's a big leap forward for all of us who work with (really) large scenes.
On my system, just 1 GB of memory, it uses almost 2.5 GB, and editing still is pretty responsive! Seems like this is an excellent way to allocate large data segmentsâ€¦ and leave it to the OS to swap away the unused chunks.
Just a couple of hours ago I've committed this system integrated in our secure malloc system. While rendering now, all texture images, shadow buffers, render result buffers and compositing buffers are using mmap, with very nice stable and not-fragmented memory results. :)
Even better; with the current tile-based rendering pipeline, it's an excellent way to balance memory to swap to disk when unused, to be able to render projects requiring quite some more memory than physically in your system.
The full article is available on the Orange Blog. A fixe for Windows is already on their way.
Update: As Diffid pointed out, only Windows suffers the same problems. Other Operating Systems seem to be fine.