* Peter Xu (pet...@redhat.com) wrote: > On Tue, Dec 01, 2020 at 06:40:55PM +0000, Dr. David Alan Gilbert wrote: > > > Yep, seems that current userfaultfd supports hugetlbfs and shared memory > > > for > > > missing pages but not for wr-protected.. > > > > For hugepages, you'd need kernel support - but also you'd want to make > > sure you write the whole hugepage at once. > > Or we can do similar things by splitting the huge pages just like when we > migrate. > > I should have overlooked these facts when I replied previusly - we do need the > same logic, but also special care on these special memory types. > > > > > For shared, there's a harder problem to ask; what happens if RAM is > > written by the other process - for postcopy, we get the other process > > to send us a userfaultfd that they have registered with their VM. > > Good point... so we should need similar things too. > > Looks like we'd better explicitly disable shmem/hugetlbfs for now from qemu > background snapshots before we have prepared these utilities, just in case it > got run on some "future" kernels and accidentally got enabled, so the snapshot > files could be corrupted ones. > > Is shmem used a lot in libvirt, or is it even a default configuration?
No, but it's used with vhost-user applications; like dpdk. Dave > -- > Peter Xu > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
