From: John Hubbard <jhubbard@nvidia.com>
To: Jann Horn <jannh@google.com>, Michal Hocko <mhocko@kernel.org>
Cc: Michael Kerrisk <mtk.manpages@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux API <linux-api@vger.kernel.org>,
Michal Hocko <mhocko@suse.com>
Subject: Re: [PATCH] mmap.2: document new MAP_FIXED_NOREPLACE flag
Date: Wed, 11 Apr 2018 13:36:21 -0700 [thread overview]
Message-ID: <827ead33-5d93-7696-9c5e-1cd04f772476@nvidia.com> (raw)
In-Reply-To: <CAG48ez3BS5EtnrhFQUGYY9MKGOUHzFbhauJQd361uTwy2pBEeg@mail.gmail.com>
On 04/11/2018 08:37 AM, Jann Horn wrote:
> On Wed, Apr 11, 2018 at 2:04 PM, <mhocko@kernel.org> wrote:
>> From: Michal Hocko <mhocko@suse.com>
>>
>> 4.17+ kernels offer a new MAP_FIXED_NOREPLACE flag which allows the caller to
>> atomicaly probe for a given address range.
>>
>> [wording heavily updated by John Hubbard <jhubbard@nvidia.com>]
>> Signed-off-by: Michal Hocko <mhocko@suse.com>
>> ---
>> Hi,
>> Andrew's sent the MAP_FIXED_NOREPLACE to Linus for the upcoming merge
>> window. So here we go with the man page update.
>>
>> man2/mmap.2 | 27 +++++++++++++++++++++++++++
>> 1 file changed, 27 insertions(+)
>>
>> diff --git a/man2/mmap.2 b/man2/mmap.2
>> index ea64eb8f0dcc..f702f3e4eba2 100644
>> --- a/man2/mmap.2
>> +++ b/man2/mmap.2
>> @@ -261,6 +261,27 @@ Examples include
>> and the PAM libraries
>> .UR http://www.linux-pam.org
>> .UE .
>> +Newer kernels
>> +(Linux 4.17 and later) have a
>> +.B MAP_FIXED_NOREPLACE
>> +option that avoids the corruption problem; if available, MAP_FIXED_NOREPLACE
>> +should be preferred over MAP_FIXED.
>
> This still looks wrong to me. There are legitimate uses for MAP_FIXED,
> and for most users of MAP_FIXED that I'm aware of, MAP_FIXED_NOREPLACE
> wouldn't work while MAP_FIXED works perfectly well.
>
> MAP_FIXED is for when you have already reserved the targeted memory
> area using another VMA; MAP_FIXED_NOREPLACE is for when you haven't.
That's a nice summary, I hope it shows up in your upcoming patch. I recall
that we went back and forth, trying to find a balance of explaining
this feature, without providing overly-elaborate examples (which I tend
toward).
> Please don't make it sound as if MAP_FIXED is always wrong.
>
Agreed.
thanks,
--
John Hubbard
NVIDIA
next prev parent reply other threads:[~2018-04-11 20:36 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-11 12:04 [PATCH] mmap.2: document new MAP_FIXED_NOREPLACE flag mhocko
2018-04-11 15:37 ` Jann Horn
2018-04-11 16:36 ` Michal Hocko
2018-04-11 16:40 ` Jann Horn
2018-04-11 17:06 ` Michal Hocko
2018-04-12 8:09 ` Michael Kerrisk (man-pages)
2018-04-12 8:10 ` Michael Kerrisk (man-pages)
2018-04-11 20:36 ` John Hubbard [this message]
2018-04-12 8:04 ` Michael Kerrisk (man-pages)
2018-04-12 8:21 ` Michal Hocko
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=827ead33-5d93-7696-9c5e-1cd04f772476@nvidia.com \
--to=jhubbard@nvidia.com \
--cc=akpm@linux-foundation.org \
--cc=jannh@google.com \
--cc=linux-api@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mhocko@kernel.org \
--cc=mhocko@suse.com \
--cc=mtk.manpages@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).