linux-kernel - Re: [patch 1/6] mmu

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Message-ID: <20080130222035.GX26420@sgi.com>
Date:	Wed, 30 Jan 2008 16:20:35 -0600
From:	Robin Holt <holt@....com>
To:	Christoph Lameter <clameter@....com>
Cc:	Jack Steiner <steiner@....com>,
	Andrea Arcangeli <andrea@...ranet.com>,
	Robin Holt <holt@....com>, Avi Kivity <avi@...ranet.com>,
	Izik Eidus <izike@...ranet.com>, Nick Piggin <npiggin@...e.de>,
	kvm-devel@...ts.sourceforge.net,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com, Hugh Dickins <hugh@...itas.com>
Subject: Re: [patch 1/6] mmu_notifier: Core code

On Wed, Jan 30, 2008 at 11:19:28AM -0800, Christoph Lameter wrote:
> On Wed, 30 Jan 2008, Jack Steiner wrote:
> 
> > Moving to a different lock solves the problem.
> 
> Well it gets us back to the issue why we removed the lock. As Robin said 
> before: If its global then we can have a huge number of tasks contending 
> for the lock on startup of a process with a large number of ranks. The 
> reason to go to mmap_sem was that it was placed in the mm_struct and so we 
> would just have a couple of contentions per mm_struct.
> 
> I'll be looking for some other way to do this.

I think Andrea's original concept of the lock in the mmu_notifier_head
structure was the best.  I agree with him that it should be a spinlock
instead of the rw_lock.

Thanks,
Robin
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