Re: [Xen-devel] netfront/netback multiqueue exhausting grants

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.01.16 at 01:29, <bob.liu@xxxxxxxxxx> wrote:

> On 01/22/2016 07:02 PM, Jan Beulich wrote:
>>>>> On 22.01.16 at 11:40, <bob.liu@xxxxxxxxxx> wrote:
>>> On 01/22/2016 03:53 PM, Jan Beulich wrote:
>>>>>>> On 22.01.16 at 04:36, <bob.liu@xxxxxxxxxx> wrote:
>>>>> By the way, do you think it's possible to make grant table support bigger 
>>>>> page e.g 64K?
>>>>> One grant-ref per 64KB instead of 4KB, this should able to reduce the 
>>>>> grant 
>>>>> entry consumption significantly.
>>>>
>>>> How would that work with an underlying page size of 4k, and pages
>>>> potentially being non-contiguous in machine address space? Besides
>>>> that the grant table hypercall interface isn't prepared to support
>>>> 64k page size, due to its use of uint16_t for the length of copy ops.
>>>
>>> Right, and I mean whether we should consider address all the place as your 
>>> mentioned.
>> 
>> Just from an abstract perspective: How would you envision to avoid
>> machine address discontiguity? Or would you want to limit such an
> 
> E.g Reserve a page pool with continuous 64KB pages, or make grant-map support 
> huge page(2MB)?
> To be honest, I haven't think much about the detail.
> 
> Do you think that's unlikely to implement?

Contiguous memory (of whatever granularity above 4k) is quite
difficult to _guarantee_ in PV guests, so yes, without you or
someone else having a fantastic new idea on how to achieve
this I indeed see this pretty unlikely a thing to come true.

Jan


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