Current kGraft implementation allows to apply new patch only when the previous one is applied to the whole system. Every task is handled separately and it needs to wait for a safe place to switch. It might take a while, especially when the task is sleeping.

Therefore it would be great to allow to apply more patches in parallel. It is not trivial because different tasks might be in different world, so the slow stub has to be clever and choose the right one without taking any lock...