Yes, I've recompiled a kernel with dm and encrypt a whole partition.
Works like a charm.

I didn't post because it needs a custom kernel (dm has to be linked to the kernel, module is not possible, afaik) and not sure people will use a new kernel.

So it's kernel-level encryption. No need for any software in theory. In practice I have also ported one tool to ease the mounting. Now I need one command to mount my enc partition.

As for truecrypt, it's another layer. I have no use of this