Re: problems with hierarchy: L4 pagers

[Neal H. Walfield]

At Tue, 18 Oct 2005 08:39:54 -0400,
Jonathan S. Shapiro wrote:
> 
> On Tue, 2005-10-18 at 10:02 +0100, Neal H. Walfield wrote:
> > At Mon, 17 Oct 2005 17:15:06 -0400,
> > Jonathan S. Shapiro wrote:
> > First, you have just multiplied the cost of any IPC involving a map
> > > operation by four additional IPCs. In essence, you have reconstructed
> > > the logic that had to be used to implement COPY on top of REVOCABLE
> > > COPY, but you haven't yet covered all of the necessary advisory
> > > messages.
> > 
> > What RPCs?  In your example, I see two base IPCs per B page fault:
> > when B faults, the kernel sends an IPC to B' and B' installs the
> > mapping by sending an IPC to B.
> 
> I see five:
> 
>   A must advice A' that it plans to send a mapping to B so
>   that A' knows to support later recovery. This is an RPC
>   operation. It requires to IPCs.
> 
>   A now transmits to B: one IPC
> 
>   B must now advice B' of the existence of the mapping.
>   This is another RPC. It requires two IPCs

I think you are describing a possible protocol to establish *how*
mappings can be reconstructed.  The protocol I tried to describe was
what happens *when* a mapping needs to be reconstructed.

Thanks,
Neal