linux-kernel - Re: [PATCH] Fix dirty page accounting in redirty_page_for

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Message-ID: <alpine.LFD.2.00.0904300914110.3395@localhost.localdomain>
Date:	Thu, 30 Apr 2009 09:16:31 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Christoph Lameter <cl@...ux.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, thomas.pi@...or.dea,
	Yuriy Lalym <ylalym@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	ltt-dev@...ts.casi.polymtl.ca, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH] Fix dirty page accounting in
 redirty_page_for_writepage()



On Thu, 30 Apr 2009, Ingo Molnar wrote:
> 
> c0436275:   64 83 05 20 5f 6a c0    addl   $0x1,%fs:0xc06a5f20
> 
> There's no atomic instructions at all - the counters here are only 
> accessed locally. They are local-irq-atomic, but not 
> cacheline-atomic.

On other architectures, you need the whole "disable preemption, 
load-locked, store-conditional, test-and-loop, enable preemption" thing. 

Or "disable interrupts, load, store, restore interrupts".

There really aren't very many architectures that can do almost 
unrestricted ALU ops in a single instruction (and thus automatically safe 
from preemption and interrupts).

			Linus
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