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

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 10/10/14 08:35, Jan Beulich wrote:
>>>> 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.

Agreed.

> 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.

This would seem sensible.

David

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