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Re: [Xen-devel] 5x dom0 memory increase from Xen/Linux 3.4/2.6.18 to 4.1/3.0.0

On Thu, Jun 16, 2011 at 01:58:25PM +0100, Anthony Wright wrote:
> I have a fairly old machine with 512M of RAM that I use for testing. Under 
> Xen 3.4 with the 2.6.18 linux kernel it would happily work with dom0_mem=50M, 
> leaving 450M for VMs. I am in the process of upgrading to Xen 4.1 with a 
> stock 3.0.0-rc3 linux kernel (with konrad's vga-support patch). This 
> combination however requires dom0_mem=250M to work leaving only 250M for the 
> VMs (if I try to set dom0_mem any lower I get a kernel panic early on in the 
> kernel boot phase).

> This is an increase of 5x between the two versions, and I wondered if there's 
> an explanation why. Is it possible to reduce the memory requirements, or do I 
> have to learn to live with it.

The SWIOTLB is taking a 64MB chunk out of it. You could lower that by 
'swiotlb=2048' or so.
Also make sure to compile the CONFIG_XEN_MAX_DOMAIN_MEMORY from 128GB down to 
say 1.

Besides that .. run with 'memblock=debug loglevel=10 initcall_debug debug' and 
see what other
regions memblock reserves that could be shrunk.
> thanks,
> Anthony Wright
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