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

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> "Xu, Dongxiao" <dongxiao.xu@xxxxxxxxx> 14.01.10 10:09 >>>
>Jan Beulich wrote:
>> it is clear that the tools still will need adjustment: The full
>> ballooning only happens from _initDomain(), and hence the
>> pre-reservation (from _constructDomain) of 4Mb would still be too
>> small for large vCPU counts. 
>
>The pre-reservation of memory size should be no relationship with
>vcpu number. As vcpu hasn't been initialized at that point. On vcpu
>initialization, the patch has ballooned the shadow size to 128 pages
>per vcpu. Did you find some piece of code that use the pre-reserved
>memory to allocate vcpu-related memory? 

Your patch adds a call to sh_set_allocation() in a call tree starting at
XEN_DOMCTL_max_vcpus. That in turn originates from the call to
xc.domain_max_vcpus() in the tools, which happens between the
pre-reservation (_constructDomain()) and the full ballooning
(_initDomain()). Hence at this point only a maximum of 4Mb (as
stated before, with an unknown fraction of it being suitable) can
be assumed to be available in Xen, but 128 vCPU-s require 64Mb.

In order to make the pre-reservation not more complicated (and error
prone), I was asking whether (and if so, how and why) this memory
really is needed this early.

Jan


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