Edge vs level triggered refers to how a change in an fd's state is reflected in userspace: level triggering will cause repeated wakeups while the condition remains true, whereas edge triggering will cause exactly one, until the monitored state flips from true to false and back again.
The new flags relate to what happens when multiple threads are waiting on the same set of file descriptors (i.e. sleeping on the same epoll FD passed as the first parameter to epoll_wait(), or having the same client FD in multiple epoll sets -- sorry I'm not sure which way around it is).
Previously the kernel had no support for waking exactly one thread to handle one event, so if there was a single set shared among a bunch of sleeping tasks, all tasks would be scheduled, causing (presumably) synchronization contention on the kernel's internal structures. The new mode ensures only a single task is woken up for an event on a single FD, even when multiple tasks are waiting on it.
The new flags relate to what happens when multiple threads are waiting on the same set of file descriptors (i.e. sleeping on the same epoll FD passed as the first parameter to epoll_wait(), or having the same client FD in multiple epoll sets -- sorry I'm not sure which way around it is).
Previously the kernel had no support for waking exactly one thread to handle one event, so if there was a single set shared among a bunch of sleeping tasks, all tasks would be scheduled, causing (presumably) synchronization contention on the kernel's internal structures. The new mode ensures only a single task is woken up for an event on a single FD, even when multiple tasks are waiting on it.