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

["JHJE (Jan Holst Jensen)" <jhje@xxxxxxxxxxxxxxx>]

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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