RE: [Xen-ia64-devel] RE: Xen/ia64 - global or per VP VHPT

["Dong, Eddie" <eddie.dong@xxxxxxxxx>]

Magenheimer, Dan (HP Labs Fort Collins) wrote:
> 
> Wow, I hadn't even realized before you mentioned it... a lVHPT is
> generally contiguous in physical memory because it has to be
> pinned by a TR (or more than one TR, but there's not many to choose
> from!).
> 
> That may not be a problem when you know in advance how many domains
> are going to run on the machine and you partition the memory in
> advance, but it's a HUGE disadvantage for per-domain VHPT in the
> highly dynamic environment we envision at HP, with domains being
> frequently created, growing, shrinking, and migrating.  E.g. creating
> a domain may require a massive defrag operation to just allocate the
> per-domain VHPT. 
> And growing/shrinking a per-domain VT dynamically is MUCH more
> difficult.
> 
> I see that as a HUGE problem for using per-domain VHPTs for VT
> domains too.  Or am I missing something?
> 
> This is an excellent example of how assumptions can influence
> design... 
> 
> Now back (finally) to my regularly scheduled weekend :-)
Dan:
        Unfortuantely, our design support the machine memory
discontiguous situation :(
        The original design we shared with you has included this. The
VHPT miss will handle this. So don't worry for this. If digging into
much details of vMMU, an HV TLB/VHPT is a must to support PMT (guest
physical to machine physical). (Oh, you may argu IA64 don't need PMT, if
this is the case, it deviates from X86 much more).
Eddie

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