Re: [Xen-devel] [PATCHv11 4/4] gnttab: use per-VCPU maptrack free lists

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.06.15 at 17:55, <david.vrabel@xxxxxxxxxx> wrote:
> On 05/06/15 15:51, Jan Beulich wrote:
>>>>> On 02.06.15 at 18:26, <david.vrabel@xxxxxxxxxx> wrote:
>>> +    /*
>>> +     * max_maptrack_frames is per domain so each VCPU gets a share of
>>> +     * the maximum, but allow at least one frame per VCPU.
>>> +     */
>>> +    if ( v->maptrack_frames
>>> +         && v->maptrack_frames >= max_maptrack_frames / 
>>> v->domain->max_vcpus )
>>> +        return -1;
>> 
>> So with e.g. max_maptrack_frames being 256 and ->max_vcpus
>> being 129 you'd potentially allow each vCPU to only have exactly
>> one page despite there being 127 more to use.
> 
> There's a limit to how many wacky combinations we can support with a
> single default limit.
> 
> With the standard defaults and 129 VCPUs:
> 
> Before
> 
> 131072 entries (256 * 4096 / 8)
> 
> After
> 
> 231168 entries (1024 / 129 * 129 * 4096 / 16)
>   1792 entries per vcpu.

And that's why I'm putting the currently proposed resource
management model under question.

Jan


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