Re: [Xen-API] Can someone explain these metrics?

[Ewan Mellor <ewan@xxxxxxxxxxxxx>]

On Tue, Mar 06, 2007 at 08:00:11PM +0530, Hetal Badheka wrote:

> Hello,
> 
> Class VM has 4 memory metrics:
> 1) memory/dynamic max (RW)
> 2) memory/dynamic min (RW)
> 3) memory/static min
> 4) memory/static max
> 5) memory/actual (Guest?s actual usage)
> 
> Questions:
> 1) What is dynamic memory? Is the "memory/dynamic max" a configuration 
> parameter that you set imposing a limit on the maximum amount of memory 
> a guest may use at runtime? In that case, what does "memory/dynamic min" 
> mean?

The dynamic values are the "target" memory settings, i.e. how much
memory the administrator would like the VM to use at the moment.  The
static_max is the value used at boot-time to size page-tables and so on.
In other words, the administrator may use the dynamic_max to change the
VM's size at runtime, up to the static_max.

We have a dynamic min and max because some people have expressed an
interest in automatic (e.g. load-sensitive) memory balancers.  With one
of these, the balancer would be allowed to float the VM's memory within
the dynamic range.  We don't actually have one of these things yet, so
Xend will force the dynamic min and dynamic max to be equal.

> 2) What does "memory/actual" pertain to? A guests usage of the real, 
> physical memory available on the box or its usage of the total memory 
> (which could be more than the physical available) that has been 
> allocated to it?

This is the actual amount of memory being consumed by the VM, as
reported by Xen.  If the VM is behaving itself, then this will move
towards the dynamic_max over time.

Note that some changes to this functionality are being implemented at
the moment.  In particular, memory/actual has moved from VM to a new
VM_metrics class.  This class is documented in the API doc, and will
soon be checked in.

Ewan.

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