linux-kernel - Re: [ofa-general] Re: [patch 0/6] MMU Notifiers V6

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Message-ID: <adaprv70yyt.fsf@cisco.com>
Date:	Fri, 08 Feb 2008 16:12:42 -0800
From:	Roland Dreier <rdreier@...co.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, andrea@...ranet.com,
	a.p.zijlstra@...llo.nl, linux-mm@...ck.org, izike@...ranet.com,
	steiner@....com, linux-kernel@...r.kernel.org, avi@...ranet.com,
	kvm-devel@...ts.sourceforge.net, daniel.blueman@...drics.com,
	Robin Holt <holt@....com>, general@...ts.openfabrics.org
Subject: Re: [ofa-general] Re: [patch 0/6] MMU Notifiers V6

 > We have done several rounds of discussion on linux-kernel about this so 
 > far and the IB folks have not shown up to join in. I have tried to make 
 > this as general as possible.

Sorry, this has been on my "things to look at" list for a while, but I
haven't gotten a chance to really understand where things are yet.

In general, this MMU notifier stuff will only be useful to a subset of
InfiniBand/RDMA hardware.  Some adapters are smart enough to handle
changing the IO virtual -> bus/physical mapping on the fly, but some
aren't.  For the dumb adapters, I think the current ib_umem_get() is
pretty close to as good as we can get: we have to keep the physical
pages pinned for as long as the adapter is allowed to DMA into the
memory region.

For the smart adapters, we just need a chance to change the adapter's
page table when the kernel/CPU's mapping changes, and naively, this
stuff looks like it would work.

Andrew, does that help?

- R.
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