Re: [Xen-devel] Memory question (again)

[Ian Pratt <Ian.Pratt@xxxxxxxxxxxx>]

> 
> I still don't understand how memory management for guest OSs work. 
> 
> What exactly is the size given to xi_create? I mean, is it the minimum 
> guaranteed size (if so, where is the absolute maximum set), or is it the 
> absoulte maximum guest can use?

When the guest Linux boots, it sizes and initialises it's mem_map
array based on the number of pages that are available to it at
startup. Thus, it effectively determines the maximum size of
memory that the domain can ever have (we could in principle use
the new Linux support for "hot swappable" memory to enable the
mem_map array to be extended, but we've yet to do this and aren't
keen).

What might be a sensible improvement to the current tools would
be the ability to be able to start a domain with less memory than
its maximum size. We could do this by having the balloon driver
grab frames very early in the boot sequence, before the domain
adds them to its free list.

This is something to consider when we update the tools for
controlling the balloon driver.

Ian


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