From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Jan Beulich" <JBeulich@suse.com>
Subject: Re: Domain Save Image Format proposal (draft B)
Date: Tue, 11 Feb 2014 13:10:38 +0000
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To: David Vrabel <david.vrabel@citrix.com>, Ian Campbell <Ian.Campbell@citrix.com>
Cc: Shriram Rajagopalan <rshriram@cs.ubc.ca>, "Xen-devel@lists.xen.org" <Xen-devel@lists.xen.org>, Ian Jackson <Ian.Jackson@eu.citrix.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>
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>>> On 11.02.14 at 13:09, Ian Campbell <Ian.Campbell@citrix.com> wrote:
> On Tue, 2014-02-11 at 11:40 +0000, David Vrabel wrote:
>> On 11/02/14 09:30, Ian Campbell wrote:
>> > On Mon, 2014-02-10 at 17:20 +0000, David Vrabel wrote:
>> >> --------------------------------------------------------------------
>> >> Field       Description
>> >> ----------- --------------------------------------------------------
>> >> count       Number of pages described in this record.
>> >>
>> >> pfn         An array of count PFNs. Bits 63-60 contain
>> >>             the XEN\_DOMCTL\_PFINFO_* value for that PFN.
>> > 
>> > Now might be a good time to remove this intertwining? I suppose 60-bits
>> > is a lot of pfn's, but if the VMs address space is sparse it isn't out
>> > of the question.
>> 
>> I don't think we want to consider systems with > 64 bits of address
>> space so 60-bits is more than enough for PFNs.
> 
> Is it? What about systems with 61..63 bits of address space?

Their PFNs would, assuming 4k page size, still only be 49..51
bits wide.

That said - if reasonably cleanly doable within such a revised save
image format, I would second Ian's desire to split the type from
the PFN. Not so much because of limited PFN space, but because
of the chance of needing to introduce further types, requiring
more than 4 bits.

Jan