When we combine pre-dump with lazy pages, we populate a part of a memory
region with data that was saved during the pre-dump. Afterwards, the
region is registered with userfaultfd and we expect to get page faults for
the parts of the region that were not yet populated. However, khugepaged
collapses the pages and the page faults we would expect do not occur.

To mitigate this problem we temporarily disable THP for the restored
process, up to the point when we register all the memory regions with
userfaultfd.

https://lists.openvz.org/pipermail/criu/2017-May/037728.htmlReported-by: Adrian Reber <areber@redhat.com>
Acked-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>