On 11/22/2017 02:19 AM, Rik van Riel wrote:
We can go with the "best" interface for what could be a relatively slow flush (fsync on a file on ssd/disk on the host), which requires that the flushing task wait on completion asynchronously.
I'd like to clarify the interface of "wait on completion asynchronously" and KVM async page fault a bit more. Current design of async-page-fault only works on RAM rather than MMIO, i.e, if the page fault caused by accessing the device memory of a emulated device, it needs to go to userspace (QEMU) which emulates the operation in vCPU's thread. As i mentioned before the memory region used for vNVDIMM flush interface should be MMIO and consider its support on other hypervisors, so we do better push this async mechanism into the flush interface design itself rather than depends on kvm async-page-fault.
