Date: Tue, 5 Jan 2010 09:17:11 -0600 (CST)
From: Christoph Lameter <cl@linux-foundation.org>
To: Arjan van de Ven <arjan@infradead.org>
cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
       "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
       Peter Zijlstra <peterz@infradead.org>,
       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>,
       Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [RFC][PATCH 6/8] mm: handle_speculative_fault()
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References: <20100104182429.833180340@chello.nl> <20100104182813.753545361@chello.nl> <20100105054536.44bf8002@infradead.org>
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On Tue, 5 Jan 2010, Arjan van de Ven wrote:

> while I appreciate the goal of reducing contention on this lock...
> wouldn't step one be to remove the page zeroing from under this lock?
> that's by far (easily by 10x I would guess) the most expensive thing
> that's done under the lock, and I would expect a first order of
> contention reduction just by having the zeroing of a page not done
> under the lock...

The main issue is cacheline bouncing. mmap sem is a rw semaphore and only
held for read during a fault.

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