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

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Message-ID: <4DF18FF0.7010503@jp.fujitsu.com>
Date:	Fri, 10 Jun 2011 12:30:56 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	peterz@...radead.org
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.

(2011/06/10 2:58), Peter Zijlstra wrote:
> 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?

Yeah, I agree this is best way. Private RO mappings is not sane and no real
world users.


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