Never heard of swappolube...

In any case, like Mentalist Traceur said, blocking I/O doesn't result in a failure, it just means the process read()s, write()s, etc.. won't return immediately, but only once there's sufficient room in the (now very small) queue.

The benefit is that some desktop application that needs to read a config file doesn't risk ended up at queue position 100, waiting for 99 I/Os to complete, because cp, tar, or samba wasn't able to burst all those writes through (write() blocked quickly).