Date: Tue, 5 Jan 2010 13:00:18 -0800 (PST)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Peter Zijlstra <peterz@infradead.org>
cc: Christoph Lameter <cl@linux-foundation.org>,
       Andi Kleen <andi@firstfloor.org>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       Minchan Kim <minchan.kim@gmail.com>,
       "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "linux-mm@kvack.org" <linux-mm@kvack.org>,
       "hugh.dickins" <hugh.dickins@tiscali.co.uk>,
       Nick Piggin <nickpiggin@yahoo.com.au>, Ingo Molnar <mingo@elte.hu>
Subject: Re: [RFC][PATCH 6/8] mm: handle_speculative_fault()
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On Tue, 5 Jan 2010, Linus Torvalds wrote:
>
> I think you need a "compare-and-exchange-2-separate-words" instruction 
> to make it work (not "cmpxchg8/16b" - literally two _different_ words).

Btw, I might be misremembering - Andy was looking at various lockless 
algorithms too. Maybe the problem was the non-local space requirement. 
There were several spin-lock variants that would be improved if we could 
pass a cookie from the 'lock' to the 'unlock'.

In fact, even the ticket locks would be improved by that, since we could 
then possibly do the unlock as a plain 'store' rather than an 'add', and 
keep the nex-owner cookie in a register over the lock rather than unlock 
by just incrementing it in the nasty lock cacheline.

		Linus
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