Groups > linux.kernel > #1200717

Re: [PATCH] user_ns: use correct check for single-threadedness

From	Ricky Zhou <ricky@rzhou.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH] user_ns: use correct check for single-threadedness
Date	2015-08-05 15:20 +0200
Message-ID	<pU6LU-2ne-3@gated-at.bofh.it> (permalink)
References	<pRgHM-7lh-27@gated-at.bofh.it> <pRkLn-4Fc-1@gated-at.bofh.it> <pRlo5-5DA-15@gated-at.bofh.it> <pU5d7-8s0-7@gated-at.bofh.it> <pU5wu-nj-5@gated-at.bofh.it>
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On Wed, Aug 5, 2015 at 4:53 AM, Kirill A. Shutemov <kirill@shutemov.name> wrote:
>> 'only' if it's multi-threaded, i.e. when some workload cares so much about
>> performance that it uses multiple threads?
>>
>> Can you see the contradiction there?
>
> I can. man 2 unshare:
>
>         CLONE_NEWUSER requires that the calling process  is  not  threaded;
>
> The workload cares so much about performance that it ignores API
> requirements. Some slow down looks like a fair price to me.
To be fair, the entire reason for this patch is that the slow path
(mm_users > 1) can happen even when the process is single-threaded. I
was concerned about how expensive current_is_single_threaded looked as
well, but didn't see any lightweight alternatives short of adding a
field to mm_struct. Do folks think it's worth going down that route
instead?

Thanks,
Ricky
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Re: [PATCH] user_ns: use correct check for single-threadedness Ingo Molnar <mingo@kernel.org> - 2015-08-05 13:40 +0200
  Re: [PATCH] user_ns: use correct check for single-threadedness "Kirill A. Shutemov" <kirill@shutemov.name> - 2015-08-05 14:00 +0200
    Re: [PATCH] user_ns: use correct check for single-threadedness Ricky Zhou <ricky@rzhou.org> - 2015-08-05 15:20 +0200

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