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

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Message-ID: <Pine.LNX.4.64.0802121653460.11628@schroedinger.engr.sgi.com>
Date:	Tue, 12 Feb 2008 16:56:45 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Roland Dreier <rdreier@...co.com>
cc:	Steve Wise <swise@...ngridcomputing.com>,
	Rik van Riel <riel@...hat.com>,
	Andrea Arcangeli <andrea@...ranet.com>, a.p.zijlstra@...llo.nl,
	izike@...ranet.com, steiner@....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, 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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