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RE: [Xen-users] Xen and distributing memory


> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Ulrich Windl
> Sent: 22 February 2007 08:31
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] Xen and distributing memory
> On 21 Feb 2007 at 11:11, Marduk wrote:
> [...]
> > I'm trying to understand how Xen's memory balloon driver works.
> [...]
> That reminds me of: Should XEN maintain multiple memory zones 
> for NUMA, and then 
> extend the memory interface to request memory from a specific 
> memory zone? I think 
> recent Linux kernels can even migrate memory pages from one 
> zone to another 
> (probably if a process has a sub-optimal page allocated, are 
> more suitable page 
> can be assigned instead).

At present Xen doesn't support NUMA, but there's been work (patches have
been submitted but not accepted) to support different memory regions
(zones or whatever one might call them) for different locations in the

The first step of this would be to give limited set of processors "local
memory" when assigning domain-memory. 

A step further would be to extend the information to give the guest-OS
information abuout which socket has which areas of memory, so that the
kernel can have a good idea of where to allocate memory. Of course, this
doesn't solve all problemns. Someone (Emmanuel Ackaroy(sp?) I think)
gave the following example: one process starts, allocating a large chunk
of memory, fills this memory with data and spawns another 3 processes,
doing some heavy calculation work on the previously allocated memory.
Without direct interfaces to allocate memory to a particular processor,
it's not possible for the OS to allocate that memory correctly... :-(

Of course, a further complication is if we have 2 VCPU's but 4
physically viable CPU's in the system. Which CPU's memory do we allocate
to which processor?

> Regards,
> Ulrich
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