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

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Date:	Fri, 08 Feb 2008 16:22:41 -0800
From:	Roland Dreier <rdreier@...co.com>
To:	Christoph Lameter <clameter@....com>
Cc:	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: [patch 0/6] MMU Notifiers V6

 > I thought the adaptor can always remove the mapping by renegotiating 
 > with the remote side? Even if its dumb then a callback could notify the 
 > driver that it may be required to tear down the mapping. We then hold the 
 > pages until we get okay by the driver that the mapping has been removed.

Of course we can always destroy the memory region but that would break
the semantics that applications expect.  Basically an application can
register some chunk of its memory and get a key that it can pass to a
remote peer to let the remote peer operate on its memory via RDMA.
And that memory region/key is expected to stay valid until there is an
application-level operation to destroy it (or until the app crashes or
gets killed, etc).

 > We could also let the unmapping fail if the driver indicates that the 
 > mapping must stay.

That would of course work -- dumb adapters would just always fail,
which might be inefficient.
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