Re: [Xen-users] domU domains with > 1GB RAM

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

This is actually a standard Linux behaviour: to use more than 1GB RAM on x86, 
you need to enable CONFIG_HIGHMEM_4G, regardless of whether it's a Xen guest 
or a native kernel.

In a XenLinux src tree do:
make ARCH=xen menuconfig

The option you want is under X86 Processor Configuration -> High memory 
support.  Select 4GB and domains using that kernel will happily deal with 
1-4GB of allocated RAM.

HTH,
Mark

On Monday 09 May 2005 15:39, JHJE (Jan Holst Jensen) wrote:
> Hi.
>
> I am a bit confused about the usage of memory above 1GB in Xen. I have
> two servers running Debian Sarge with Xen 2.0.5 installed on top of
> that. Both claim to have only 900 MB memory when booting Debian Sarge
> (not Xen) although both servers have 4 GB physical memory.
>
> My initial reaction was not to care, since I assumed that this was just
> a quirk of the stock Debian kernel. And it seems that when booting into
> Xen I can use all 4 GB, at least I can boot three domains with 1000 MB,
> 1500 MB mem and 1000 MB respectively:
>
>   xen-test:/machines# xm list
>   Name              Id  Mem(MB)  CPU  State  Time(s)  Console
>   Domain-0           0      123    0  r----    102.7
>   debian-sarge       9     1000    1  -b---      1.1    9609
>   debian2-sarge     10     1500    0  -b---      6.0    9610
>   rh9-jhje          11      999    1  -b---      6.1    9611
>
> However, even though "xm list" will report that a domU is assigned 1500
> MB memory, when logging into the domain and doing "cat /proc/meminfo" it
> only sees about 900 MB. This is regardless of whether I boot a 2.4 or
> 2.6 domU kernel:
>
>   debian2-sarge:~# cat /proc/meminfo
>   MemTotal:       904376 kB
>   MemFree:        891328 kB
>
> Do I have to somehow tell the domU kernel the memory size as a boot
> parameter, or will I have to build my own domU kernels ?
>
> Cheers
> -- Jan Holst Jensen, Novo Nordisk A/S, Denmark
>
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