@raph BY the way, enjoying the whole discussion of your renderer because it sounds like all the same problems we had with the Larrabee renderer.
We had a tile-based renderer, also for load-balancing reasons, and we also had problems with potentially massive intermediate buffers. Even though the cores were general x86 cores that could indeed call malloc() in the middle of things (though note there's no backing store if you run out!), the overhead of that is huge, so you try to avoid it.