[PATCH man-pages 4/5] userfaultfd.2: add note about asynchronios events delivery

From: Mike Rapoport
Date: Mon May 01 2017 - 01:44:41 EST

Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
man2/userfaultfd.2 | 12 ++++++++++++
1 file changed, 12 insertions(+)

diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2
index 8b89162..f177bba 100644
--- a/man2/userfaultfd.2
+++ b/man2/userfaultfd.2
@@ -112,6 +112,18 @@ created for the child process,
which allows userfaultfd monitor to perform user-space paging
for the child process.

+Unlike page faults which have to be synchronous and require
+explicit or implicit wakeup,
+all other events are delivered asynchronously and
+the non-cooperative process resumes execution as
+soon as manager executes
+.BR read(2).
+The userfaultfd manager should carefully synchronize calls
+to UFFDIO_COPY with the events processing.
+The current asynchronous model of the event delivery is optimal for
+single threaded non-cooperative userfaultfd manager implementations.
.\" FIXME elaborate about non-cooperating mode, describe its limitations
.\" for kernels before 4.11, features added in 4.11
.\" and limitations remaining in 4.11