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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

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
libxl__build_hvm).
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 -
videoram_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
VMs?

 
> 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
allocations.

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