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Re: [Xen-devel] RFC: [0/2] Remove netloop by lazy copying in netback

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>, Isaku Yamahata <yamahata@xxxxxxxxxxxxx>, Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] RFC: [0/2] Remove netloop by lazy copying in netback
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Tue, 27 Mar 2007 08:51:15 +0100
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On 27/3/07 08:36, "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx> wrote:

> This is quite a shame, since the swap-grant-mapping-for-memory hypercall
> simply is not very nice. What if we wanted to swap a grant mapping for
> another grant mapping in future? Or some other kind of mapping? We end up
> needing a new, complicated, grant-table hypercall every time. Or in six
> months time we decide this wasn't such a good idea, implement another
> scheme, but have this special-purpose grant-table hypercall hanging around
> unused forever more.
> Could we shatter the ia64 guest large mappings easily? They have no benefit
> on Xen anyway apart from some inconsequential memory saving.

Also bear in mind the plan to avoid the grant mapping at all in the
direct-to-wire transmit case. This also will rely on a #PF (or some other
fault, potentially) if the guest tries to access that pseudophysical page of
memory. If we can work out a way to make this work on ia64 then the
delayed-copy implementation problems are solved too.

 -- Keir

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