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From: Robin Holt <holt@sgi.com>
To: Christoph Lameter <clameter@sgi.com>
Cc: Robin Holt <holt@sgi.com>, Andrea Arcangeli <andrea@qumranet.com>,
	Avi Kivity <avi@qumranet.com>, Izik Eidus <izike@qumranet.com>,
	kvm-devel@lists.sourceforge.net,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	steiner@sgi.com, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, daniel.blueman@quadrics.com
Subject: Re: [patch 2/4] mmu_notifier: Callbacks to invalidate address ranges
Date: Fri, 1 Feb 2008 18:21:45 -0600	[thread overview]
Message-ID: <20080202002145.GA17211@sgi.com> (raw)
In-Reply-To: <Pine.LNX.4.64.0802011602360.21158@schroedinger.engr.sgi.com>

On Fri, Feb 01, 2008 at 04:05:08PM -0800, Christoph Lameter wrote:
> On Fri, 1 Feb 2008, Robin Holt wrote:
> 
> > On Fri, Feb 01, 2008 at 03:19:32PM -0800, Christoph Lameter wrote:
> > > On Fri, 1 Feb 2008, Robin Holt wrote:
> > > 
> > > > We are getting this callout when we transition the pte from a read-only
> > > > to read-write.  Jack and I can not see a reason we would need that
> > > > callout.  It is causing problems for xpmem in that a write fault goes
> > > > to get_user_pages which gets back to do_wp_page that does the callout.
> > > 
> > > Right. You placed it there in the first place. So we can drop the code 
> > > from do_wp_page?
> > 
> > No, we need a callout when we are becoming more restrictive, but not
> > when becoming more permissive.  I would have to guess that is the case
> > for any of these callouts.  It is for both GRU and XPMEM.  I would
> > expect the same is true for KVM, but would like a ruling from Andrea on
> > that.
> 
> do_wp_page is entered when the pte shows that the page is not writeable 
> and it makes the page writable in some situations. Then we do not 
> invalidate the remote reference.
> 
> However, when we do COW then a *new* page is put in place of the existing 
> readonly page. At that point we need to remove the remote pte that is 
> readonly. Then we install a new pte pointing to a *different* page that is 
> writable.
> 
> Are you saying that you get the callback when transitioning from a read 
> only to a read write pte on the *same* page?

I believe that is what we saw.  We have not put in any more debug
information yet.  I will try to squeze it in this weekend.  Otherwise,
I will probably have to wait until early Monday.

Thanks
Robin

  reply	other threads:[~2008-02-02  0:21 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-01  5:04 [patch 0/4] [RFC] EMMU Notifiers V5 Christoph Lameter
2008-02-01  5:04 ` [patch 1/4] mmu_notifier: Core code Christoph Lameter
2008-02-01 10:55   ` Robin Holt
2008-02-01 11:04     ` Robin Holt
2008-02-01 19:14     ` Christoph Lameter
2008-02-01  5:04 ` [patch 2/4] mmu_notifier: Callbacks to invalidate address ranges Christoph Lameter
2008-02-01 10:49   ` Robin Holt
2008-02-01 19:14     ` Christoph Lameter
2008-02-01 22:09   ` Robin Holt
2008-02-01 23:19     ` Christoph Lameter
2008-02-01 23:35       ` Robin Holt
2008-02-02  0:05         ` Christoph Lameter
2008-02-02  0:21           ` Robin Holt [this message]
2008-02-02  0:38             ` Robin Holt
2008-02-03  2:23         ` Andrea Arcangeli
2008-02-01  5:04 ` [patch 3/4] mmu_notifier: invalidate_page callbacks Christoph Lameter
2008-02-01  5:04 ` [patch 4/4] mmu_notifier: Support for driverws with revers maps (f.e. for XPmem) Christoph Lameter
2008-02-01 11:58 ` Extending mmu_notifiers to handle __xip_unmap in a sleepable context? Robin Holt
2008-02-01 12:10   ` Robin Holt
2008-02-01 19:17   ` Christoph Lameter
2008-02-03  1:39 ` [patch 0/4] [RFC] EMMU Notifiers V5 Andrea Arcangeli
2008-02-03 13:41 ` Robin Holt
  -- strict thread matches above, loose matches on Subject: below --
2008-01-25  5:56 [patch 0/4] [RFC] MMU Notifiers V1 Christoph Lameter
2008-01-25  5:56 ` [patch 2/4] mmu_notifier: Callbacks to invalidate address ranges Christoph Lameter

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