Re: [Xen-devel] pre-reservation of memory for domain creation

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

It's either that or stub out the feature (return to previos #VCPUs limit) I
think.

 -- Keir

On 13/01/2010 02:34, "Xu, Dongxiao" <dongxiao.xu@xxxxxxxxx> wrote:

> If we didn't add this change, as Keir said, Xen will crash during destruction
> of partially-created domain.
> However I didn't noticed the toolstack and shadow_min_acceptable_pages() side
> at that time...
> For now, should we adjust the shadow pre-alloc size to match
> shadow_min_acceptable_pages() and modify toolstack accordingly?
> 
> Thanks!
> Dongxiao
> 
> Jan Beulich wrote:
>>>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 12.01.10 16:53 >>>
>>> On 12/01/2010 15:32, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
>>> 
>>>> Also - how did that fixed amount get determined?
>>>> shadow_min_acceptable_pages() says 128 pages per vCPU, but 4Mb
>>>> (1024 pages) is not matching this (given that it ought to be fine
>>>> for 128 vCPU-s), just as the old value of 1Mb wasn't matching the
>>>> supposed need of 32 vCPU-s.
>>> 
>>> I'm not sure I really believe the toolstack comment. As you say, it
>>> wasn't correct before or after the patch we're talking about.
>> 
>> The tool stack comment was correct before that patch; it isn't now.
>> The size in shadow_enable() doesn't match
>> shadow_min_acceptable_pages(), but that's all hypervisor code.
>> 
>> And that's also no answer to the question on where the particular
>> value came from (and namely why it being much smaller than what
>> shadow_min_acceptable_pages() would determine still isn't going
>> to be a problem).
>> 
>>>> And btw., I think that papering over a Xen crash during
>>>> destruction of partially-created domain is rather bad a thing to do.
>>> 
>>> Depends on whether domain-creation failure at the point it failed --
>>> and due to inadequate pre-reservation -- is expected and allowed for
>>> by the HVM paging logic.
>> 
>> So you say it's acceptable for a flaw in the tools (exposed during
>> guest creation) to bring down the whole machine?
>> 
>> Jan



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