linux-kernel - Re: [patch 1/1] schedule removal of FUTEX

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Message-id: <454874AD.2070607@cosmosbay.com>
Date:	Wed, 01 Nov 2006 11:19:25 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org, drepper@...hat.com,
	mingo@...e.hu, tglx@...utronix.de
Subject: Re: [patch 1/1] schedule removal of FUTEX_FD

Rusty Russell a écrit :
> On Tue, 2006-10-31 at 15:09 -0800, akpm@...l.org wrote:
>> From: Andrew Morton <akpm@...l.org>
>>
>> Apparently FUTEX_FD is unfixably racy and nothing uses it (or if it does, it
>> shouldn't).
>>
>> Add a warning printk, give any remaining users six months to migrate off it.
> 
> This makes sense.  FUTEX_FD was for the NGPT project which did userspace
> threading, and hence couldn't block.  It was always kind of a hack
> (although unfixably racy isn't quite right, it depends on usage).
> 
> However, the existence of FUTEX_FD is what made Ingo complain that we
> couldn't simply pin the futex page in memory, because now a process
> could pin one page per fd.  Removing it would seem to indicate that we
> can return to a much simpler scheme of (1) pinning a page when someone
> does futex_wait, and (2) simply comparing futexes by physical address.
> 
> Now, I realize with some dismay that simplicity is no longer a futex
> feature, but it might be worth considering?

Hum... I am not sure playing MM games is good... really...

This discussion reminds me I posted a patch some time ago that got no comments 
from the community.

http://lkml.org/lkml/2006/8/9/26

Eric

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