Re: (XEN) page_alloc.c:1148:d0 Over-allocation for domain 0: 694017 > 694016

[Konrad Rzeszutek Wilk <konrad@darnok.org>]

On Fri, Apr 27, 2012 at 10:31:22AM -0400, Konrad Rzeszutek Wilk wrote:
> > How would that be? 2711MiB = 2776064kiB, which 446k off the value
> > above. And apart from that, the value above isn't even divisible by 4
> 
> I messed up on that. Redid the numbers and I was off.
> 
> > (i.e. not an even number of pages).
> 
> To make this a bit easier I used 'dom0_max=max:3G', which means
> (with this swiss-cheese type E820 on this Intel box):
> 
> [    0.000000] Released 75745 pages of unused memory
> 
> so I should have 75745 pages left to play with. But what I found is that
> I can only go up to 786415 which is 17 pages short of the 786432 goal.
> 
> Here are the steps:
> 
> $cat `find /sys -name current_kb`
> 2842816
> $echo $((3*1024*1024))
> 3145728
> $echo "3145728" > `find /sys -name target_kb`
> $cat `find /sys -name current_kb`
> 3145660
> $xl dmesg | tail
> (XEN) page_alloc.c:1148:d0 Over-allocation for domain 0: 786433 (786432) > 786432
> (XEN) memory.c:133:d0 Could not allocate order=0 extent: id=0 memflags=0 (0 of 17)
> 
> > > Any ideas of what that might be? Could it be the shared_info, hypercall page,
> > > start_info, xenconsole and some other ones are the magic 6 pages which
> > > inhibit how much we can balloon up to?
> > 
> > Not likely: The hypercall page is in kernel (image) memory, and there's
> > no console page at all fro Dom0.
> 
> 17 pages.. Hmm

I am still not exactly sure what the problem is, but by running this on
various machines I found that I can be off by 1,2,3, 4 or 17 pages. It
looked to vary based on the amount of ACPI tables that showed up in MADT.

So I think what is happening is that the initial domain gets the ACPI
regions (which are shared) accounted in its d->tot_pages. I can't
pinpoint the exact piece of code in the hypervisor for this.

But what I did do on the Linux side was using the current_reservation
hypercall (so d->tot_pages) and based on that would populate exactly
up to start_info->nr_pages - d->tot_pages pages and did not get any of
those errors.

> > 
> > Jan
> 
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