From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Vrabel <david.vrabel@citrix.com>
Subject: Re: [PATCHv11 4/4] gnttab: use per-VCPU maptrack free
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Date: Fri, 5 Jun 2015 17:42:52 +0100
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To: Jan Beulich <JBeulich@suse.com>
Cc: xen-devel <xen-devel@lists.xenproject.org>, Malcolm Crossley <malcolm.crossley@citrix.com>, Keir Fraser <keir@xen.org>, Ian Campbell <ian.campbell@citrix.com>, Tim Deegan <tim@xen.org>
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On 05/06/15 17:11, Jan Beulich wrote:
>>>> On 05.06.15 at 17:55, <david.vrabel@citrix.com> wrote:
>> On 05/06/15 15:51, Jan Beulich wrote:
>>>>>> On 02.06.15 at 18:26, <david.vrabel@citrix.com> 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.

The new default of 1024 frames ensures that with any number of VCPUs
results in the domain having /more/ entries than then old default (256
frames).

It's not at all clear what you want here.  Can you provide a proposal?

David