Re: [Xen-devel] Design doc of adding ACPI support for arm64 on Xen - version 2

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Wed, 2015-08-12 at 10:42 +0800, Shannon Zhao wrote:
> 
> On 2015/8/12 0:01, Julien Grall wrote:
> > On 11/08/15 16:19, Ian Campbell wrote:
> > > > IIRC we talked about it few months ago and you said that using 
> > > > balloon
> > > > page will split in 4K the 1G/2M mapping done in the stage-2 p2m.
> > > 
> > > Did I? Odd because I'm also of the opinion that alloc_ballooned_pages
> > > should operate in chunks of 2M at the hypercall layer and keep any
> > > resulting spare 4K pages on a free list to use for future such 
> > > allocations.
> > 
> > That from what I recall from an IRL talk.
> > 
> > Anyway, I've looked in my archive to see why we decided to keep the
> > grant table parameters (in Xen ACPI table at this point). We were not
> > sure that the domain as all the key in hand in order to find memory 
> > hole.
> > 
> > I think it's quite important to not think only about Linux but all 
> > other
> > Operating Systems. If we ever require a parameters later, it would mean
> > that the OS won't be able to run as DOM0 on older Xen.
> > 
> > Linux is using ballooned page, which means loosing ~128KB (default of
> > the grant table on ARM) of memory because we never give back the page 
> > to
> > Xen due the 1:1 mapping. Although I guess this is not a big deal as 
> > it's
> > quite small and Linux, as said by David, will support memory hotplug 
> > soon.
> > 
> > FreeBSD is using memory hole in the address space so there is no issue 
> > here.
> > 
> > So I guess we could skip this parameters as 128KB doesn't seem to be a
> > big deal.
> > 
> > > IOW it should avoid such shattering where it can.
> > 
> > That would work too.
> > 
> 
> So use xlated_setup_gnttab_pages for both DT and ACPI?

I think we might as well, yes.

Ian.


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