Re: [PATCH v2 2/5] userfaultfd: non-cooperative: add event for memory unmaps

From: Andrew Morton
Date: Tue Jan 31 2017 - 19:40:44 EST

On Fri, 27 Jan 2017 20:44:30 +0200 Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> wrote:

> When a non-cooperative userfaultfd monitor copies pages in the background,
> it may encounter regions that were already unmapped. Addition of
> UFFD_EVENT_UNMAP allows the uffd monitor to track precisely changes in the
> virtual memory layout.
> Since there might be different uffd contexts for the affected VMAs, we
> first should create a temporary representation for the unmap event for each
> uffd context and then notify them one by one to the appropriate userfault
> file descriptors.
> The event notification occurs after the mmap_sem has been released.

I was going to bug you about not updating
Documentation/vm/userfaultfd.txt but the UFFD_FEATURE flags aren't