Re: [PATCH] x86: set dom0's default maximum reservation to the initial number of pages

[David Vrabel <david.vrabel@citrix.com>]

On 21/03/12 10:14, Jan Beulich wrote:
> On 21.03.12 at 10:58, David Vrabel <david.vrabel@citrix.com> wrote:
>> The docs still need updating and I think the min:MMM option should be
>> deprecated.
> 
> Why should we deprecate min:? It can be useful when combined with
> other sub-options, can't it?

Not convinced of its utility but it does do something, so yes, it should
be kept.

>>>> This change means that with Linux 3.0.5 and later kernels,
>>>> dom0_mem=512M has the same result as older, 'classic Xen' kernels. The
>>>> older kernels used the initial number of pages to set the maximum
>>>> number of pages and did not query the hypervisor for the maximum
>>>> reservation.
>>>
>>> If the pv-ops kernels behave differently in this aspect than the forward
>>> ported ones, then it should really be the newer one to get adjusted to
>>> the original behavior (if so intended), unless the old behavior was
>>> completely insane. Adjusting the hypervisor for a shortcoming(?) in a
>>> particular implementation of a Dom0 kernel doesn't seem to be the right
>>> route - please also consider non-Linux Dom0 kernels that might expect
>>> the current behavior.
>>
>> The old behaviour did not allow dom0 to balloon up beyond the initial
>> allocation so we don't what to go back to that.
> 
> In pv-ops Linux Dom0 you mean? While I can't speak of non-Linux,
> ballooning up beyond the initial allocation works fine in the legacy
> and forward ported kernels.

Perhaps I'm looking at a XenServer specific limitation.

David