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

["Xu, Dongxiao" <dongxiao.xu@xxxxxxxxx>]

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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