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

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Message-ID: <20080422132143.GS12709@duo.random>
Date:	Tue, 22 Apr 2008 15:21:43 +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 08:01:20AM -0500, Robin Holt wrote:
> On Tue, Apr 22, 2008 at 02:00:56PM +0200, Andrea Arcangeli wrote:
> > 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;
> 
> I don't think you need it here since invalidate_range_count is already
> elevated which will accomplish the same effect.

Agreed, seqlock only in range_end should be enough. BTW, the fact
seqlock is needed regardless of invalidate_page existing or not,
really makes invalidate_page a no brainer not just from the core VM
point of view, but from the driver point of view too. The
kvm_page_fault logic would be the same even if I remove
invalidate_page from the mmu notifier patch but it'd run slower both
when armed and disarmed.
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