[anarazel]

> I think a key property of RCU as traditionally presented is that writers always wait for global quiescence directly after their write, and then immediately delete the garbage.

A rather common, in my opinion, way to use something like rcu is to delay freeing (or reusing) memory to the next grace period, without blocking until then. E.g. in the kernel you can use kfree_rcu(..); instead of synchronize_rcu(); kfree(..); for that. That's basically what the epoch based approach does with a the lists of to-be-freed allocations.