linux-kernel - Re: [PATCH 0 of 9] mmu notifier #v12

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Date:	Tue, 22 Apr 2008 14:00:56 +0200
From:	Andrea Arcangeli <andrea@...ranet.com>
To:	Robin Holt <holt@....com>
Cc:	Christoph Lameter <clameter@....com>, akpm@...ux-foundation.org,
	Nick Piggin <npiggin@...e.de>,
	Steve Wise <swise@...ngridcomputing.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-mm@...ck.org,
	Kanoj Sarcar <kanojsarcar@...oo.com>,
	Roland Dreier <rdreier@...co.com>,
	Jack Steiner <steiner@....com>, linux-kernel@...r.kernel.org,
	Avi Kivity <avi@...ranet.com>, kvm-devel@...ts.sourceforge.net,
	general@...ts.openfabrics.org, Hugh Dickins <hugh@...itas.com>
Subject: Re: [PATCH 0 of 9] mmu notifier #v12

On Tue, Apr 22, 2008 at 09:20:26AM +0200, Andrea Arcangeli wrote:
>     invalidate_range_start {
> 	spin_lock(&kvm->mmu_lock);
> 
> 	kvm->invalidate_range_count++;
> 	rmap-invalidate of sptes in range
> 

	write_seqlock; write_sequnlock;

> 	spin_unlock(&kvm->mmu_lock)
>     }
> 
>     invalidate_range_end {
> 	spin_lock(&kvm->mmu_lock);
> 
> 	kvm->invalidate_range_count--;


	write_seqlock; write_sequnlock;

> 
> 	spin_unlock(&kvm->mmu_lock)
>     }

Robin correctly pointed out by PM there should be a seqlock in
range_begin/end too like corrected above.

I guess it's better to use an explicit sequence counter so we avoid an
useless spinlock of the write_seqlock (mmu_lock is enough already in
all places) and so we can increase it with a single op with +=2 in the
range_begin/end. The above is a lower-perf version of the final
locking but simpler for reading purposes.
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