Re: [Xen-devel] [RFC/PATCH v2] XENMEM_claim_pages (subop of existing) hypercall

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 20.11.12 at 18:52, Dan Magenheimer <dan.magenheimer@xxxxxxxxxx> wrote:
>>  From: Tim Deegan [mailto:tim@xxxxxxx]
>> Subject: Re: [Xen-devel] [RFC/PATCH v2] XENMEM_claim_pages (subop of 
> existing) hypercall
>> 
>> At 08:33 -0800 on 20 Nov (1353400380), Dan Magenheimer wrote:
>> > I agree it's possible, just saying it's not trivial... one has to
>> > account not only for superpages system-wide (which isn't currently
>> > done) but a mix of unclaimed superpages and unclaimed order==0 pages
>> > per-domain.  Especially since that would improve launch of only a small
>> > and shrinking class of domains (PV && superpages=1 && mem="huge"),
>> > can we please consider it a possible future enhancement, not a showstopper?
>> 
>> Please, no.  Either you need this benighted hypercall, or you don't.
>> If you really need it, do it properly.
> 
> Hi Tim --
> 
> I must respectfully disagree.
> 
> For years, Xen has been accepting features that work on a 64-bit
> hypervisor but not on a 32-bit hypervisor.  And new features such
> as memory-sharing/paging _could_ be designed to help PV domains and
> have completely ignored PV but have still been accepted.  There is
> clearly precedent for new features that don't enhance every
> possible case.
> 
> The claim feature dramatically decreases a real customer problem in
> the vast majority of our customer environments with no loss of
> functionality in the small remaining percentage.  This real problem
> is getting continually worse as system physical RAM and domain memory
> requirements increase.  So, yes, _we_ do need it.

A meaningful difference is that those other features have tools
side users, while you add (from the perspective of the Xen tree)
dead code. That is, it wouldn't have any chance of getting checked
for correctness when committed (other than for not breaking
existing code), and it will bit rot pretty quickly. Or did you mean
to supply tools side integration before expecting this to be
considered for applying?

In any case, while the hypervisor side changes look acceptable,
I'm afraid that without (mostly) convincing (almost) all of the
maintainers, there's no perspective of this getting committed.

Jan


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