linux-kernel - Re: [RFC MM] Accessors for mm locking

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Date:	Thu, 5 Nov 2009 15:57:23 -0500 (EST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
cc:	npiggin@...e.de, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"hugh.dickins@...cali.co.uk" <hugh.dickins@...cali.co.uk>
Subject: Re: [RFC MM] Accessors for mm locking

On Thu, 5 Nov 2009, Andi Kleen wrote:

> My assumption was that a suitable scalable lock (or rather multi locks)
> would need to know about the virtual address, or at least the VMA.
> As in doing range locking for different address space areas.

Not sure why the address would matter. The main problem right now is that
there are cachelines in mm_struct that are bouncing for concurrent page faults
etc. Ranges wont help if you need to serialize access to mm_struct.

> So this simple abstraction doesn't seem to be enough to really experiment?

Look at the next patch which gives a rough implementation of using per cpu
counters for read locking instead of the rw semaphore.
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