Re: [Xen-users] RAM disapeared?

[Simon Hobson <linux@xxxxxxxxxxxxxxxx>]

Heiko wrote:

> I have some dom0 which have 8GB RAM, but when I look with xm list, it
> just shows me 6GB,
> I need to setup some new VM, each with 1GB, so I should have with 3VM
> still 5GB free,
> but im only seeing 3GB.
> Can I just create 2 new VM with each 1GB and still have 3GB for the dom0?
>
> #xm top
> xentop - 11:31:17   Xen 3.1.0-53.1.14.el5
> 4 domains: 1 running, 3 blocked, 0 paused, 0 crashed, 0 dying, 0 shutdown
> Mem: 8386888k total, 6336300k used, 2050588k free    CPUs: 8 @ 2327MHz
>
> #xm list:
> Name                                      ID Mem(MiB) VCPUs State   Time(s)
> Domain-0                                   0     3057     8 r----- 1265671.8
> xxx-vm2                              12      999     2 r-----   4074.0
> xxxx-vm2                 11      999     2 -b----    620.2
> xxxxxx-vm2                           7      999     2 -b---- 238229.7
It could be that the combination of OS & hardware limits the host to 
"under 4G" for itself, and so that's all that shows up. The rest of 
the ram could well be available to be divvied up between guests 
though.
You can also explicitly limit host ram usage, and I believe this is 
recommended for two reasons :
1) Some kernel tables are sized according to memory at boot time - so 
when the memory is ballooned down, the kernel tables are bigger than 
they need to be.
2) When I upgraded Xen at home over Christmas, I came up with an 
error (can't recall what) which was specific to running Dom0 without 
a memory limit.
You limit Dom0 memory by adding "dom0_mem=<some value>" to your Xen 
kernel line, like this :
>  kernel      /xen-3.2-1-amd64.gz dom0_mem=512M


--
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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