Re: [XenPPC] Re: xen heap size

[Hollis Blanchard <hollisb@xxxxxxxxxx>]

On Fri, 2007-02-23 at 11:12 -0600, Ryan Harper wrote:
> * Hollis Blanchard <hollisb@xxxxxxxxxx> [2007-02-23 10:58]:
> > On Fri, 2007-02-23 at 10:21 -0600, Ryan Harper wrote:
> > > 
> > > The other method I was going to look into was to allocate dom0's rma,
> > > and then calculation would look like:
> > > 
> > >    dom0_start_mfn = page_to_mfn(d->arch.rma_base);
> > >    dom0_overlap = (dom0_start_mfn + dom0_nrpages - rma_sz) -
> > > IO_SIZE_PAGES;
> > >    
> > > Any other good way to figure how much of dom0's allocation will fall
> > > within 2-4G IO hole?
> > 
> > Why are you looking for another approach? What's wrong with this
> > solution?
> 
> I was hoping I'd find this:
> 
> xen/arch/powerpc/memory.c:145
> 
>     xenheap_phys_end = xh_pages << PAGE_SHIFT;
>     printk("End of Xen Area: %luMiB (%luKiB)\n",
>            xenheap_phys_end >> 20, xenheap_phys_end >> 10);
> 
> 
> which marks the end of the xen area; just what I was looking for.
> 
> Now I can do:
> 
>    /* overlap in pages into 2G-4G IO range (if any) */
>    dom0_overlap = ((xenheap_phys_end >> PAGE_SHIFT) + dom0_nrpages) -
>                   IO_SIZE_PAGES;

You're assuming that the Xen heap ends exactly where dom0 will begin
(i.e. where dom0's RMA is allocated), which is not the case. From your
boot log, we see this:
        (XEN) End of Xen Area: 144MiB (147456KiB)
        ...
        (XEN) xenheap: 000000000006d000 - 0000000000400000
        (XEN) xenheap: 0000000000c46000 - 0000000009000000
        (XEN) Xen Heap: 135MiB (138548KiB)

xenheap_phys_end is 144MB (0x9000000), and when you subtract the space
from the middle (e.g. occupied by Xen itself), you end up with a total
of 135MB.

In this case, dom0's RMA will be allocated at 192MB (0xc000000), and the
space from 144MB (0x9000000) to 192MB will be assigned to the domain
heap.

-- 
Hollis Blanchard
IBM Linux Technology Center


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