On Tue, 14 Nov 2017 11:56:34 -0800 Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > Until there is a solution to the dma-to-dax vs truncate problem it is > not safe to allow long standing memory registrations against > filesytem-dax vmas. Device-dax vmas do not have this problem and are > explicitly allowed. > > This is temporary until a "memory registration with layout-lease" > mechanism can be implemented for the affected sub-systems (RDMA and > V4L2). Sounds like that will be unpleasant. Do we really need it to be that complex? Can we get away with simply failing the get_user_pages() request? Or are there significant usecases for RDMA and V4L to play with DAX memory?