Re: [Xen-devel] One question about the hypercall to translate gfn to mfn.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.12.14 at 10:05, <kevin.tian@xxxxxxxxx> wrote:
> yes, definitely host RAM is the upper limit, and what I'm concerning here
> is how to reserve (at boot time) or allocate (on-demand) such large PFN
> resource, w/o collision with other PFN reservation usage (ballooning
> should be fine since it's operating existing RAM ranges in dom0 e820
> table).

I don't think ballooning is restricted to the regions named RAM in
Dom0's E820 table (at least it shouldn't be, and wasn't in the
classic Xen kernels).

> Maybe we can reserve a big-enough reserved region in dom0's 
> e820 table at boot time, for all PFN reservation usages, and then allocate
> them on-demand for specific usages?

What would "big enough" here mean (i.e. how would one determine
the needed size up front)? Plus any form of allocation would need a
reasonable approach to avoid fragmentation. And anyway I'm not
getting what position you're on: Do you expect to be able to fit
everything that needs mapping into the available mapping space (as
your reply above seems to imply) or do you think there won't be
enough mapping space (as earlier replies of yours appeared to
indicate)?

Jan


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