Re: [Xen-devel] Memory oversubscription

[Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>]

> On Tue, 14 Sep 2004, Todd Jones wrote:
> 
> > 2. Inflate a balloon in that domain and return say 40MB back to Xen
> 
> OK, how does this work ?
> 
> I've searched through the documentation and it doesn't
> seem to be an xm option either ... ;)

For the moment, you can only control the amount of memory that a
domain is using from within the domain itself using
/proc/xen/memory_target

Whatever size (in bytes) you enter in this field, the domain will
try to adjust itself to this size. If it's currently too big, it
will try to grab free pages and hand them back to Xen. If it
needs to grow, it will request new pages from Xen.

We need to add a new xend control message that allow dom0 to
directly control what the memory target for another domain should
be. We then need to add a new xm command to enable it to be
controlled.

The maximum size the domain can grow to is bounded by the minimum
of that set by "xm maxmem" and the size of the mem_map array that
the domain has. There's a new "maxmem=" linux kernel command line
option to enable a domain to be started with a bigger mem_map
array than is required for its initial memory allocation. Once
hot-plug memory is standard we'll be able to do away with the
maxmem option.

Hmm. Thinking about it, I'm not sure whether either memory_target
or maxmem have been ported from 2.4 to 2.6.  Any volunteers?
[This would also be a good opportunity to do a slight cleanup to
the balloon driver and thread the 'released' pages in a linked
list through the mem_map array rather than scanning the P2M table.]

Ian







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