Yeah... the sudden paging in also has been noted as a source of latency in the network-oriented software. But that's the problem with our current state of the APIs and their implementations: ideally, you'd have as many independent threads of executions as you want/need, and every time one of them initiates some "blocking" operation, it is quickly end efficiently scheduled, and another ready-to-run thread is switched in. Native threads don't give you that context-switching efficiency, and user-space threads can accidentally cause an underlying native thread block even on "read a non-local variable".