linux-kernel - Re: [PATCH 4/5] Add a sysconf syscall

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Message-ID: <BANLkTikDX0G5EWZ7w1Ob_7YBZpA5xDvGQw@mail.gmail.com>
Date:	Mon, 16 May 2011 13:06:10 -0400
From:	Andrew Lutomirski <luto@....edu>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	libc-alpha@...rceware.org, Andi Kleen <ak@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 4/5] Add a sysconf syscall

On Mon, May 16, 2011 at 12:08 PM, Andi Kleen <andi@...stfloor.org> wrote:
>> You could also add a vsyscall function and have that function pull the
>> values from vvar data.  It would be very fast (i.e. almost as fast as
>> mmaping some data) and it would be more portable.
>
> vvar is a global. The variable data in sysconf is per thread
> (and not even per mm)
>
> Even if you ignore the semantic problem of thread versus mm, you would
> need a new writable page per process and update it any time
> the rlimits and other information is updated.
>
> On the other hand my solution is dead simple and already solves
> the problem.

True.  I should read the entire list of variables before making
suggestions that won't work.  :)

--Andy

>
> -Andi
>
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