Re: [Xen-devel] [PATCH 0/5] xen: better grant v2 support

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.08.17 at 20:05, <jgross@xxxxxxxx> wrote:
> Currently Linux has no support for grant v2 as this would reduce the
> maximum number of active grants by a factor of 2 compared to v1,
> because the number of possible grants are limited by the allowed number
> of grant frames and grant entries of v2 need twice as much bytes as
> those of v1.
> 
> Unfortunately grant v2 is the only way to support either guests with
> more than 16TB memory size or PV guests with memory above the 16TB
> border, as grant v1 limits the frame number to be 32 bits wide.
> 
> In order to remove the disadvantage of grant v2 this patch series
> enables configuring different maximum grant frame numbers for v1 and
> v2.

But that does imply higher memory footprint of such a guest in Xen,
doesn't it? The limit, after all, is there to bound resource use of
DomU-s.  I wonder whether we shouldn't make any such increase
dependent on first putting in place proper accounting of the memory
used for individual domains.

Jan


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