[Xen-devel] RE: Tmem vs order>0 allocation, workaround RFC

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

> From: Jan Beulich [mailto:JBeulich@xxxxxxxxxx]
> Subject: RE: Tmem vs order>0 allocation, workaround RFC
> 
> >>> Dan Magenheimer <dan.magenheimer@xxxxxxxxxx> 16.02.10 16:05 >>>
> >Under what circumstances does dom0 require single-page-below-4G
> >allocations?  Is it only for bounce buffers for PCI passthrough
> >of old devices with 32-bit addressing limitations?  Or am I
> >missing a much more common case?
> 
> Not just for pass-through; all devices only supporting 32-bit
> addressing would have such requirements, and particularly common
> ones are display adapters which have DRM/AGP drivers loaded for
> them.

Right, but those are statically allocated when dom0 is
launched, not dynamically allocated later after tmem
(or other memory allocation technologies) begin working,
right?  Whereas pass-through devices would need below-4G
pages later?

(And 32-bit devices in a 1TB machine seems a bit of a
stretch, but I suppose it is good to enumerate all the
cases.)

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