Date: Thu, 7 Jan 2010 12:13:28 -0800 (PST)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Christoph Lameter <cl@linux-foundation.org>
cc: Peter Zijlstra <peterz@infradead.org>,
       Arjan van de Ven <arjan@infradead.org>,
       "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
       KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "linux-mm@kvack.org" <linux-mm@kvack.org>,
       "minchan.kim@gmail.com" <minchan.kim@gmail.com>,
       "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 Thu, 7 Jan 2010, Linus Torvalds wrote:
> 
> Again, it doesn't matter. Old or new - if some other thread looks up the 
> vma, either is fine.

Btw, don't get me wrong. That patch may compile (I checked it), but I am 
not in any way claiming that it is anything else than a total throw-away 
"this is something we could look at doing" suggestion.

For example, I'm not at all wedded to using 'mm->page_table_lock': I in 
fact wanted to use a per-vma lock, but I picked a lock we already had. The 
fact that picking a lock we already had also means that it serializes page 
table updates (sometimes) is actually a downside, not a good thing. 

So the patch was meant to get people thinking about alternatives, rather 
than anything else.

The point being that there are things we can play with on mmap_sem, that 
don't involve getting rid of it - just being a bit more aggressive in how 
we use it.

			Linus
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