Re: [Xen-devel] Xen ballooning interface

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Aug 13, 2018 at 04:27:06PM +0200, Juergen Gross wrote:
> On 13/08/18 16:12, Roger Pau Monné wrote:
> > On Mon, Aug 13, 2018 at 03:06:10PM +0200, Juergen Gross wrote:
> > Currently as you say there's a difference between the xenstore target
> > and the guest memory map, because some memory is used by the firmware.
> > In order to solve this the toolstack won't provide an absolute memory
> > target but instead a relative one to the guest that contains the
> > balloon size.
> > 
> > But the toolstack interface (xl) still uses mem-set which is an
> > absolute value. How is the toolstack going to accurately calculate the
> > balloon size without knowing the extra memory used by the firmware?
> 
> mem-set will make use of the current allocation the tools know about and
> add/subtract the difference to the new value to/from the target balloon
> size. I don't think firmware will eat away memory when the guest OS is
> already running. :-)
> 
> The main difference to today's situation is that the same component
> which did the initial calculation how much memory should be allocated is
> doing the math in case of ballooning now. So no guesswork any longer.

Right, it doesn't matter how much memory is used by the firmware
because the guest is going to balloon down an exact amount given by
the toolstack, so that at the end of the ballooning the used memory is
going to match the toolstack expectations.

Roger.

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