Re: [Xen-devel] Assigning contiguous memory to a driver domain

[Rafal Wojtczuk <rafal@xxxxxxxxxxxxxxxxxxxxxx>]

On Wed, Sep 15, 2010 at 02:49:37PM +0100, Jan Beulich wrote:
> >>> On 15.09.10 at 14:06, Rafal Wojtczuk <rafal@xxxxxxxxxxxxxxxxxxxxxx> wrote:
> > It is not too convincing, either. Firstly, assuming there is no dom0mem
> > parameter to Xen, dom0 gets all memory initially, so when dom0 boots the
> > first time, Xen free memory = 0 ? And drivers load fine.
> 
> Xen reserves 1/16th of the memory (up to 128Mb) in this case for this
> very purpose. Otherwise, Dom0 would neither be able to set up its
> swiotlb nor would any coherent/consistent allocations work.
I see.

> > Secondly, by default on Fedora, the pm-utils scripts tell NetworkManager to
> > turn off networking just before entering S3 sleep, and NetworkManager downs 
> > all
> > interfaces. It brings them up on resume. And apparently there are some
> > drivers, like tg3, that needs to alloc when bringing up the device. Still,
> > suspend/resume works when all devices are assigned to dom0.
> 
> Because on suspend the driver frees the memory which on resume
> it will allocate back?
I am a bit lost.
By "frees the memory" you mean "return contiguous memory to Xen free memory" ?
Does it really work this way ?
If so, it requires nonzero Xen free memory ? And that is why when I do
"ifconfig eth0 down; ifconfig eth0 up" in the driver domain the second one
fails ?

Regards,
Rafal Wojtczuk

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