Re: [Xen-devel] Can't always start 32 bit domains after 64 bit domains

[Sarah Newman <srn@xxxxxxxxx>]

On 11/21/2016 05:21 AM, Andrew Cooper wrote:
> On 21/11/16 10:05, Jan Beulich wrote:

>>>> Back in the xend days someone here had invented a (crude) mechanism
>>>> to set aside memory for 32-bit PV domains, but I don't think dealing with
>>>> this situation in xl has ever seen any interest.
>>> If I wanted to add that, where would it go?
>> I don't know, that's a question for xl folks I guess.
> 
> IIRC, given no other constraints, the Xen heap allocation allocates from
> the top down to help this exact case.

Yes, that's what I thought it did too, though I can't find my source 
information for that.

> 
> I suspect that libxl's preference towards NUMA allocation of domains
> interferes with this, by adding a NUMA constraints to memory allocations
> for 64bit PV guests.

I ran xl info -n (which I didn't know about before) and that shows the problem 
much more clearly.

If that's the reason not all the higher memory is being used first: is a 
potential workaround to pin 64 bit domains to the second physical core on
boot, and 32 bit domains to the first physical core on boot, and then change 
the allowed cores with 'xl vcpu-pin' after the domain is loaded?

Thanks, Sarah

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