GHC's great space profiling tools don't appear to be much help when your leaked memory is stored in references (IORefs, StablePtrs, etc). I had a real-life case where the allocation profile showed me where the leaked data came from, and I could guess that it was being held by some reference, but I couldn't tell which one. Retainer set profiling showed a big suspicious entry for "SYSTEM", but I couldn't find any way to pinpoint the problem. (It ended up being a missing freeStablePtr in hsgnutls, found by code inspection.) Here's a contrived example that just allocates a bunch of IORefs: import Control.Monad import Data.IORef main = repeatM (newIORef [1,2,3]) repeatM io = liftM2 (:) io (repeatM io) Retainer set profiling shows everything in "SYSTEM". None of the other profiling methods say anything interesting either. What I'd like to get, I think, is (1) your memory is being held in IORefs (2) allocated by this cost center and (3) being retained by this cost center. I guess I'm looking for something like a memory profiler for a traditional language. But I haven't really thought it all out (and I don't even understand everything the existing profiles tell me). Are there some tricks I've missed for this sort of debugging? And perchance would this be an interesting GHC hackathon subject? Andrew