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

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Date:	Tue, 5 Jan 2010 05:45:36 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	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>,
	cl@...ux-foundation.org,
	"hugh.dickins" <hugh.dickins@...cali.co.uk>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RFC][PATCH 6/8] mm: handle_speculative_fault()

On Mon, 04 Jan 2010 19:24:35 +0100
Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> Generic speculative fault handler, tries to service a pagefault
> without holding mmap_sem.


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...


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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