Writing kernel modules in Haskell

I'm not sure about the GC strategies you're referring to, but it is at least possible to implement a compacting GC algorithm in real-time. The trick is that you don't try to set an upper bound on the time required to traverse the entire active set; rather, you perform part of the GC at every allocation, and include some translation/bookkeeping when reading or writing pointer fields. The amount of work performed per allocation determines the amount of extra memory needed vs. your maximum active set: more time spent on GC per allocation results in more efficient use of memory.