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Re: [Xen-devel] [PATCH 4 of 4] xenpaging: initial libxl support

On Mon, 21 Nov 2011, Olaf Hering wrote:
> On Mon, Nov 21, Stefano Stabellini wrote:
> > what if tot_memkb is bigger than target_memkb? Or even bigger than
> > max_memkb?
> tot_memkb is unrelated to target_memkb, also somewhat unrelated to
> max_memkb.

At build time ballooning is not active yet and target_memkb represents
the amount of memory available to the VM plus the videoram (see
As a consequence I think that tot_memkb cannot be higher than
target_memkb - videoram_memkb (that is build_start in the diagram). 

So, what is going to happen if tot_memkb is higher than target_memkb -
Also, what is going to happen if it is lower?

> xenpaging will look at tot_memkb value (at "memory/target-tot_pages" to
> be precise) and try to reach that number of domain->tot_pages. If the
> tot_memkb number is larger than max_memkb nothing will happen.

How is it going to reach the tot_pages target? Where is it going to take
the memory from? Is it going to automatically page out memory from other

> Right now there is not much checking anyway, memory=1024 maxmem=1 in the
> config is accepted in my testing.
That is a correct configuration: it means that the domain has 1024MB of
RAM but it cannot allocate any more (maximum allocation limit being 1MB).
maxmem doesn't influence the current memory of the VM, only future

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