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 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).

Ian.


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