Re: [Xen-ia64-devel] [PATCH] Use saner dom0 memory and vcpu defaults, don't panic on over-allocation

[Jarod Wilson <jwilson@xxxxxxxxxx>]

Isaku Yamahata wrote:
> On Tue, Jul 31, 2007 at 10:43:44PM -0600, Alex Williamson wrote:
>>> +       /* maximum available memory for dom0 */
>>> +       max_dom0_pages = avail_domheap_pages() -
>>> +                        min(avail_domheap_pages() /
>>> +                        16UL, 512UL << (20 - PAGE_SHIFT)) ;
>>    I assume this heuristic came from Akio's patch in the thread you
>> referenced; can anyone explain how this was derived and why it's
>> necessary?  It looks like a fairly random fudge factor.  Thanks,
> 
> I guess it comes from compute_dom0_nr_pages() under arch/x86.
> However I don't know why compute_dom0_nr_pages() is so.
> Anyway It should be different for ia64. While I'm guessing the most
> dominant factor is the p2m table, domain0 building process should
> be revised for the correct estimation.

The version above does seem to work well for me on all the boxes I've
tested it on, but I'm definitely all ears for how exactly to obtain a
better calculation. I'm not familiar enough with the memory layout to
easily come up with it myself, so anyone else has a suggestion there,
please do speak up.

> BTW alloc_dom0_size() may be confusing because it doesn't allocate anymore.
> How about calc_dom0_size()? 
> This isn't essential. very minor issue. Just for my preference.

That change works for me.

-- 
Jarod Wilson
jwilson@xxxxxxxxxx

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