Re: [Xen-devel] Proposed new "memory capacity claim" hypercall/feature

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

> From: Ian Campbell [mailto:ian.campbell@xxxxxxxxxx]
> Sent: Monday, November 05, 2012 3:30 AM
> To: Dan Magenheimer
> Cc: Tim (Xen.org); Keir (Xen.org); Jan Beulich; Olaf Hering; George Dunlap; 
> Ian Jackson; George
> Shuklin; DarioFaggioli; xen-devel@xxxxxxxxxxxxx; Konrad Wilk; Kurt Hackel; 
> Mukesh Rathor; Zhigang Wang
> Subject: Re: Proposed new "memory capacity claim" hypercall/feature
> 
> On Mon, 2012-11-05 at 00:23 +0000, Dan Magenheimer wrote:
> > There is no "free up enough memory on that host". Tmem doesn't start
> > ballooning out enough memory to start the VM... the guests are
> > responsible for doing the ballooning and it is _already done_.  The
> > machine either has sufficient free+freeable memory or it does not;
> 
> How does one go about deciding which host in a multi thousand host
> deployment to try the claim hypercall on?

I don't get paid enough to solve that problem :-)

VM placement (both for new domains and migration due to
load-balancing and power-management) is dependent on a
number of factors currently involving CPU utilization,
SAN utilization, and LAN utilization, I think using
historical trends on streams of sampled statistics.  This
is very non-deterministic as all of these factors may
vary dramatically within a sampling interval.

Adding free+freeable memory to this just adds one more
such statistic.  Actually two, as it is probably best to
track free separately from freeable since a candidate
host that has enough free memory should have preference
over one with freeable memory.

Sorry if that's not very satisfying but anything beyond that
meager description is outside of my area of expertise.

Dan

P.S. I don't think I've ever said _thousands_ of physical
hosts, just hundreds (with thousands of VMs).  Honestly
I don't know the upper support bound for an Oracle VM
"server pool" (which is what we call the collection of
hundreds of physical machines)... it may be thousands.

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