[$] The next steps for userfaultfd()

The userfaultfd() system callallows user space to intervene in the handling of page faults. As AndreaArcangeli and Mike Rapaport described in a 2017 Linux Storage, Filesystem,and Memory-Management Summit session dedicated to the subject,userfaultfd() was originally created to help with the livemigration of virtual machines between physical hosts. It allows pages tobe copied to the new host on demand, after the machine itself has beenmoved, leading to faster, more predictable migrations. Work onuserfaultfd() is not finished, though; there are a number of otherfeatures that developers would like to add.