Re: [Xen-devel] [PATCH v3 1/5] xen: introduce two different max_nr_dom0/domU_grant_frames parameters

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.10.14 at 18:42, <david.vrabel@xxxxxxxxxx> wrote:
> On 08/10/14 17:01, Stefano Stabellini wrote:
>> On Wed, 8 Oct 2014, David Vrabel wrote:
>>> On 08/10/14 14:00, Stefano Stabellini wrote:
>>>> Remove max_nr_grant_frames, both variable and preprocessor symbol.
>>>> Introduce two global variables max_nr_dom0_grant_frames and
>>>> max_nr_domU_grant_frames, separately configurable via the Xen command line
>>>> option "gnttab_max_nr_frames".
>>>
>>> Why?  I can't think of a sensible use case for this and you don't list
>>> one.  dom0 doesn't really use grants so its current number grant frames
>>> is usually 1 so it doesn't seem useful to restrict it differently.
>> 
>> See the recent discussion with Jan:
>> 
>> http://marc.info/?l=xen-devel&m=141260825209210 
> 
> I still don't see a use case.  Either:
> 
> a) dom0 is the driver domain and doesn't need a large number of grants.
> 
> or
> 
> b) dom0 has a frontend driver, then the driver domain will have to scan
> dom0's grant table thus dom0's grant table must be sized the same as domUs.

Looks like you missed that max_nr_maptrack_frames(), which I
think you agree is needed in Dom0, also depends on
max_nr_grant_frames. Question then of course is whether the
distinction should be made at that: Allow controlling grant frames
and maptrack frames separately, rather than Dom0 and DomU.

Jan


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