Re: [Xen-devel] [PATCH v3 8/8] xen: arm: allocate more than one bank for 1:1 domain 0 if needed

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2014-06-30 at 17:20 +0100, Julien Grall wrote:
> On 06/30/2014 05:14 PM, Ian Campbell wrote:
> > On Mon, 2014-06-30 at 17:10 +0100, Julien Grall wrote:
> >> Hi Ian,
> >>
> >> On 06/30/2014 04:58 PM, Ian Campbell wrote:
> >>> On Fri, 2014-06-27 at 14:09 +0100, Ian Campbell wrote:
> >>>> On Fri, 2014-06-27 at 14:04 +0100, Julien Grall wrote:
> >>>>>
> >>>>> On 27/06/14 14:01, Ian Campbell wrote:
> >>>>>>> Futhermore, it looks like we always allocate memory from the top of 
> >>>>>>> this
> >>>>>>> zone. Is it normal?
> >>>>>>
> >>>>>> Normal behaviour is to allocate from as high as possible so I'm not
> >>>>>> surprised that applies with a zone as well.
> >>>>>
> >>>>> For DOM0 bank allocation, shouldn't we try to allocate as lower as 
> >>>>> possible? If not, we may not be able to create a second bank for dom0.
> >>>>
> >>>> The loop over bits is supposed to help there, but it's not as effective
> >>>> with higher addresses I suppose.
> >>>>
> >>>> We'd need a new flag fore the allocate. Which is doable I guess. I'll
> >>>> give it a try.
> >>>
> >>> It's a bit tricky and involves messing with the guts of the page
> >>> allocator, which I'd rather avoid...
> >>>
> >>> We do allow allocations to be merged onto the start of bank 0, which in
> >>> the normal case is what I would expect to happen, although it isn't
> >>> guaranteed. In that case we would try higher addresses and might find
> >>> enough RAM there.
> >>>
> >>> I suppose I could relax the constraint a bit and allow new banks in
> >>> front of bank zero if they were >= 128MB (say).
> >>
> >> So, replacing the bank zero by the new bank, right? IIRC, some Linux
> >> version are requiring the bank to be ordered.
> > 
> > Inserting the new bank before, retaining the ordering.
> 
> Thanks, this plan sounds good!

I've implemented it in the obvious way, but I can't for the life of me
get the scenario to actually occur despite playing with module load
location, fdt rsvmem, mem= and dom0_mem=.

I suppose that gives us some confidence that this is not going to happen
very often...

Ian.






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