Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion

[Dan Williams]

On Mon, Jul 24, 2017 at 8:48 AM, Jan Kara <address@hidden> wrote:
> On Mon 24-07-17 08:10:05, Dan Williams wrote:
>> On Mon, Jul 24, 2017 at 5:37 AM, Jan Kara <address@hidden> wrote:
[..]
>> This approach would turn into a full fsync on the host. The question
>> in my mind is whether there is any optimization to be had by trapping
>> dax_flush() and calling msync() on host ranges, but Jan is right
>> trapping blkdev_issue_flush() and turning around and calling host
>> fsync() is the most straightforward approach that does not need driver
>> interface changes. The dax_flush() approach would need to modify it
>> into a async completion interface.
>
> If the backing device on the host is actually a normal block device or an
> image file, doing full fsync() is the most efficient implementation
> anyway...

Ah, ok, great. That was the gap in my understanding.