linux-kernel - RE: [ofa-general] Re: Demand paging for memory regions

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Message-ID: <Pine.LNX.4.64.0802121656550.11628@schroedinger.engr.sgi.com>
Date:	Tue, 12 Feb 2008 16:57:19 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Felix Marti <felix@...lsio.com>
cc:	Roland Dreier <rdreier@...co.com>, Rik van Riel <riel@...hat.com>,
	steiner@....com, Andrea Arcangeli <andrea@...ranet.com>,
	a.p.zijlstra@...llo.nl, izike@...ranet.com,
	linux-kernel@...r.kernel.org, avi@...ranet.com, linux-mm@...ck.org,
	daniel.blueman@...drics.com, Robin Holt <holt@....com>,
	general@...ts.openfabrics.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	kvm-devel@...ts.sourceforge.net
Subject: RE: [ofa-general] Re: Demand paging for memory regions

On Tue, 12 Feb 2008, Felix Marti wrote:

> > I don't know anything about the T3 internals, but it's not clear that
> > you could do this without a new chip design in general.  Lot's of RDMA
> > devices were designed expecting that when a packet arrives, the HW can
> > look up the bus address for a given memory region/offset and place the
> > packet immediately.  It seems like a major change to be able to
> > generate a "page fault" interrupt when a page isn't present, or even
> > just wait to scatter some data until the host finishes updating page
> > tables when the HW needs the translation.
> 
> That is correct, not a change we can make for T3. We could, in theory,
> deal with changing mappings though. The change would need to be
> synchronized though: the VM would need to tell us which mapping were
> about to change and the driver would then need to disable DMA to/from
> it, do the change and resume DMA.

Right. That is the intend of the patchset.
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