Date: Tue, 12 Feb 2008 16:56:45 -0800 (PST)
From: Christoph Lameter <clameter@sgi.com>
To: Roland Dreier <rdreier@cisco.com>
cc: Steve Wise <swise@opengridcomputing.com>, Rik van Riel <riel@redhat.com>,
       Andrea Arcangeli <andrea@qumranet.com>, a.p.zijlstra@chello.nl,
       izike@qumranet.com, steiner@sgi.com, linux-kernel@vger.kernel.org,
       avi@qumranet.com, linux-mm@kvack.org, daniel.blueman@quadrics.com,
       Robin Holt <holt@sgi.com>, general@lists.openfabrics.org,
       Andrew Morton <akpm@linux-foundation.org>,
       kvm-devel@lists.sourceforge.net
Subject: Re: [ofa-general] Re: Demand paging for memory regions
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On Tue, 12 Feb 2008, Roland Dreier 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.

Well if the VM wants to invalidate a page then the remote end first has to 
remove its mapping. 

If a page has been removed then the remote end would encounter a fault and 
then would have to wait for the local end to reestablish its mapping 
before proceeding.

So the packet would only be generated when both ends are in sync.


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