On Tue, May 30, 2017 at 5:17 AM, Paolo Bonzini <pbonz...@redhat.com> wrote: > > > On 26/05/2017 16:24, Dan Williams wrote: >>> For DAX device only, QEMU can figure out the proper alignment by >>> itself. However, I'm not sure whether there are other non-DAX cases >>> requiring non-default alignment, so I think it's better to just add an >>> interface (i.e. align attribute) in QEMU and let other management >>> tools (e.g. libvirt?) fill a proper value. >> I can't imagine any cases where you would want to specify an >> alignment. If it's regular file mmap any alignment is fine, and if >> it's device-dax only the configured alignment of the device instance >> is allowed. So, I don't think this should be a configurable option, >> just read it from the device instance and you're done. > > A 2M or 1G alignment lets KVM use EPT hugepages if the host physical > addresses are contiguous and 2M- or 1G-aligned. > > QEMU only does this for hugetlbfs currently, where the requirement on > the host physical addresses is always satisfied. Would the same apply > to NVDIMM device DAX? >
Yes, I believe it is similar. Device-dax guarantees and enforces (mmap area must be aligned) a given fault granularity.
