linux-kernel - Re: [patch 5/6] mmu_notifier: Support for drivers with revers maps (f.e. for XPmem)

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Message-ID: <20080220090548.GH11391@sgi.com>
Date:	Wed, 20 Feb 2008 03:05:48 -0600
From:	Robin Holt <holt@....com>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Robin Holt <holt@....com>, Christoph Lameter <clameter@....com>,
	akpm@...ux-foundation.org, Andrea Arcangeli <andrea@...ranet.com>,
	Avi Kivity <avi@...ranet.com>, Izik Eidus <izike@...ranet.com>,
	kvm-devel@...ts.sourceforge.net,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	general@...ts.openfabrics.org,
	Steve Wise <swise@...ngridcomputing.com>,
	Roland Dreier <rdreier@...co.com>,
	Kanoj Sarcar <kanojsarcar@...oo.com>, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com
Subject: Re: [patch 5/6] mmu_notifier: Support for drivers with revers maps
	(f.e. for XPmem)

On Wed, Feb 20, 2008 at 03:00:36AM -0600, Robin Holt wrote:
> On Wed, Feb 20, 2008 at 02:51:45PM +1100, Nick Piggin wrote:
> > On Wednesday 20 February 2008 14:12, Robin Holt wrote:
> > > For XPMEM, we do not currently allow file backed
> > > mapping pages from being exported so we should never reach this condition.
> > > It has been an issue since day 1.  We have operated with that assumption
> > > for 6 years and have not had issues with that assumption.  The user of
> > > xpmem is MPT and it controls the communication buffers so it is reasonable
> > > to expect this type of behavior.
> > 
> > OK, that makes things simpler.
> > 
> > So why can't you export a device from your xpmem driver, which
> > can be mmap()ed to give out "anonymous" memory pages to be used
> > for these communication buffers?
> 
> Because we need to have heap and stack available as well.  MPT does
> not control all the communication buffer areas.  I haven't checked, but
> this is the same problem that IB will have.  I believe they are actually
> allowing any memory region be accessible, but I am not sure of that.

I should have read my work email first.  I had gotten an email from
one of our MPT developers saying they would love it if they could share
file backed memory areas as well as it would help them with their MPI-IO
functions which currently need to do multiple copy steps.  Not sure how
high of a priority I am going to be able to make that.


Thanks,
Robin
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