On 05/02/2017 11:46 AM, Mike Rapoport wrote: > On Mon, May 01, 2017 at 08:33:45PM +0200, Michael Kerrisk (man-pages) wrote: >> Hi Mike, >> >> On 05/01/2017 07:43 AM, Mike Rapoport wrote: >>> Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> >> >> Thanks. Applied. One question below. >> >>> --- >>> 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. >> >> The preceding paragraph feels incomplete. It seems like you want to make >> a point with that last sentence, but the point is not explicit. What's >> missing? > > I've copied both from Documentation/vm/userfaulftfd.txt, and there we also > talk about possibility of addition of synchronous events delivery and > that makes the paragraph above to seem crippled :) > The major point here is that current events delivery model could be > problematic for multi-threaded monitor. I even suspect that it would be > impossible to ensure synchronization between page faults and non-page > fault events in multi-threaded monitor. Okay -- thanks for the info. I've noted it, but won't make changes any changes to the page for now. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
