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? Thanks, Paolo
