linux-kernel - Re: Change in functionality of futex() system call.

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Message-ID: <1307642307.3941.92.camel@twins>
Date:	Thu, 09 Jun 2011 19:58:27 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	dvhart@...ux.intel.com, david@...advisors.com,
	kyle@...fetthome.net, luto@....edu, eric.dumazet@...il.com,
	linux-kernel@...r.kernel.org, sbohrer@...advisors.com,
	zvonler@...advisors.com, hughd@...gle.com, tglx@...utronix.de,
	mingo@...e.hu
Subject: Re: Change in functionality of futex() system call.

On Thu, 2011-06-09 at 14:05 +0200, Peter Zijlstra wrote:
> On Thu, 2011-06-09 at 20:37 +0900, KOSAKI Motohiro wrote:
> > 1) check the pte of the target address is RW attribute.
> >  2-1) if yes, it has no COW chance. we can safely use gup result.
> >  2-2) if no, we have to fallback slow vma walk. maybe, it's okey.
> >       both RO mappings and COW are rare situation. 
> 
> Not so, clean file pages are RO, even if the vma is writable. We use the
> fault to track dirty state with.

Why can't something like
http://marc.info/?l=linux-kernel&m=130737669810421 work once you restore
the rw argument?
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