On 04/05/2017 15:02, Pavel Dovgalyuk wrote: >> Understood. And what checkpoint will you be waiting for during drain, >> causing a deadlock? > Every checkpoint processes the queue, but none of them are invoked, > because iothread (which invokes all the checkpoints) is waiting for the end > of the drain. > > And we cannot add a checkpoint into the drain, because then vmstop will > affect the behavior of the guest.
But it does affect the behavior already when RR is off. And it shouldn't be a problem if it does in record mode (as long as the effect can be replayed). If RR cannot do drain reliably, not even in record mode, that is a huge problem because a lot of block layer operations assume they can. Paolo
