On 05/02/2017 11:22 AM, Mike Rapoport wrote: > On Mon, May 01, 2017 at 08:34:16PM +0200, Michael Kerrisk (man-pages) wrote: >> Hi Mike, >> >> On 04/28/2017 11:45 AM, Mike Rapoprt wrote: >>> >>> >>> On April 27, 2017 8:26:16 PM GMT+03:00, "Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx> wrote: >>>> Hi Mike, >>>> >>>> I've applied this, but have some questions/points I think >>>> further clarification. >>>> >>>> On 04/27/2017 04:14 PM, Mike Rapoport wrote: >>>>> Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> >>>>> --- >>>>> man2/userfaultfd.2 | 135 >>>> ++++++++++++++++++++++++++++++++++++++++++++++++++--- >>>>> 1 file changed, 128 insertions(+), 7 deletions(-) >>>>> >>>>> diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2 >>>>> index cfea5cb..44af3e4 100644 >>>>> --- a/man2/userfaultfd.2 >>>>> +++ b/man2/userfaultfd.2 >>>>> @@ -75,7 +75,7 @@ flag in >>>>> .PP >>>>> When the last file descriptor referring to a userfaultfd object is >>>> closed, >>>>> all memory ranges that were registered with the object are >>>> unregistered >>>>> -and unread page-fault events are flushed. >>>>> +and unread events are flushed. >>>>> .\" >>>>> .SS Usage >>>>> The userfaultfd mechanism is designed to allow a thread in a >>>> multithreaded >>>>> @@ -99,6 +99,20 @@ In such non-cooperative mode, >>>>> the process that monitors userfaultfd and handles page faults >>>>> needs to be aware of the changes in the virtual memory layout >>>>> of the faulting process to avoid memory corruption. >>>>> + >>>>> +Starting from Linux 4.11, >>>>> +userfaultfd may notify the fault-handling threads about changes >>>>> +in the virtual memory layout of the faulting process. >>>>> +In addition, if the faulting process invokes >>>>> +.BR fork (2) >>>>> +system call, >>>>> +the userfaultfd objects associated with the parent may be duplicated >>>>> +into the child process and the userfaultfd monitor will be notified >>>>> +about the file descriptor associated with the userfault objects >>>> >>>> What does "notified about the file descriptor" mean? >>> >>> Well, seems that I've made this one really awkward :) >>> When the monitored process forks, all the userfault objects >>> associated with it are duplicated into the child process. For each >>> duplicated object, userfault generates event of type UFFD_EVENT_FORK >>> and the uffdio_msg for this event contains the file descriptor that >>> should be used to manipulate the duplicated userfault object. >>> Hope this clarifies. >> >> Yes, it's clearer now. >> >> Mostly what was needed here was a forward reference that mentions >> UFFD_EVENT_FORK explicitly. I added that, and also enhanced the >> text on UFFD_EVENT_FORK a little. >> >> Also, it's not just fork(2) for which UFFD_EVENT_FORK is generated, >> right? It can also be a clone(2) cal that does not specify >> CLONE_VM, right? > > Yes. > >> Could you review my changes in commit 522ab2ff6fc9010432a >> to make sure they are okay. > > Yes, thats correct and with your updates the text is much clearer. Thanks. Thanks for checking! 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>
