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

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

> 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.

Considering maintenance, adding 100% claim support for remaining
near-obsolescent domains will (IMHO) unnecessarily clutter both
the hypervisor and the toolstack, with very little net value
to real customers.

So, in my opinion, it _is_ done properly already, just not
obsessively.

Dan

P.S. Did you mean "beknighted"?  Or are you referring to your
omniscient toolstack as enlightened and Oracle's toolstack as
ignorant?  As a fan of etymology and wordplay, I'm curious...

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