Re: [PATCH] KVM simplified virtio balloon driver

[Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>]

On Thursday 17 January 2008 13:14:58 Anthony Liguori wrote:
> Rusty Russell wrote:
> > +static struct virtio_device_id id_table[] = {
> > +	{ VIRTIO_ID_BALLOON, VIRTIO_DEV_ANY_ID},
>
> Could use a space after VIRTIO_DEV_ANY_ID

Thanks, fixed.

> > +		__free_page(page);
> > +		vb->num_pages--;
> > +		totalram_pages++;
>
> Do we really want to modify totalram_pages in this driver?  The only
> other place that I see that modifies it is in mm/memory_hotplug and it
> also modifies other things (like num_physpages).  The cmm driver doesn't
> touch totalram_pages.

I don't think there's a standard here, they're all ad-hoc (eg. no locking)  
Modifying totalram_pages has the nice effect of showing up in "free" in the 
guest.

We should probably not modify num_physpages, because some places seem to use 
it as an address space limit.  But we should probably fix all those 
networking size heuristics to use totalram_pages instead of num_physpages.

> It would be very useful too to write vb->num_pages into the config space
> whenever it was updated.  This way, the host can easily keep track of
> where the guest is at in terms of ballooning.

OTOH it's currently pretty obvious (and usually fatal) if the guest has 
trouble meeting the balloon requirements.  A serious host needs a way of 
detecting stress in the guest anyway, which this doesn't offer until it's too 
late...

Rusty.

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