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

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Message-ID: <5fb9e169-5d92-2fe8-cc59-5c68cfb6be72@gmail.com>
Date:   Mon, 1 May 2017 20:33:45 +0200
From:   "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:     Mike Rapoport <rppt@...ux.vnet.ibm.com>
Cc:     mtk.manpages@...il.com, Andrea Arcangeli <aarcange@...hat.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-man@...r.kernel.org
Subject: Re: [PATCH man-pages 4/5] userfaultfd.2: add note about asynchronios
 events delivery

Hi Mike,

On 05/01/2017 07:43 AM, Mike Rapoport wrote:
> Signed-off-by: Mike Rapoport <rppt@...ux.vnet.ibm.com>

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?

> +
>  .\" 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
> 

Cheers,

Michael



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/