> Barriers are pretty cheap; [0] claims a 0.9% time overhead for a card-marking barrier common in generational collection and 1.6% for an object-logging barrier which is also useful for concurrent collection. Apparently they're cheaper nowadays, but the results aren't published yet [1]. That's not to say that the barriers are free, but it seems feasible that collector optimisations could still cover that ground.

A quick look at the paper indicates that researchers were able to find cases in which the cost was as low as 0.9%. I don't think it's a good idea to operate as if that is the cost.