linux-kernel - Re: [RFC][PATCH 6/8] mm: handle_speculative

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Message-ID: <alpine.LFD.2.00.1001071208550.7821@localhost.localdomain>
Date:	Thu, 7 Jan 2010 12:13:28 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Christoph Lameter <cl@...ux-foundation.org>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Arjan van de Ven <arjan@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"minchan.kim@...il.com" <minchan.kim@...il.com>,
	"hugh.dickins" <hugh.dickins@...cali.co.uk>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC][PATCH 6/8] mm: handle_speculative_fault()

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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