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[Xen-users] how much memory does the hypervisor need

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] how much memory does the hypervisor need
From: Philipp Schmid <lists@xxxxxxxxxxx>
Date: Tue, 17 Feb 2009 22:29:05 +0100
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I wonder how much memory the hypervisor needs. I have the following vms running:

xen26:~# xm list
Name ID Mem VCPUs State Time(s) Domain-0 0 725 1 r----- 2064.7 g-hlsan9ib 1 4096 4 - b---- 160.9 g-lp549ugs 19 1024 4 - b---- 83.0 g-lpjj78e9 2 1024 2 - b---- 156.1 g-nt731fct 17 2048 2 - b---- 116.5 g-resl3iqi 4 2048 4 - b---- 326.7 g-rujbc3il 5 2048 4 - b---- 192.6 g-v72lkt0b 6 1024 2 - b---- 197.5

725+4096+1024+1024+2048+2048+2048+1024 = 14037mb

dom0 has fixed 725mb of memory, the server has 16gb of memory.

if try to launch another 2048mb vm i get the following:

xen26:~# xm create /etc/xen/g-ida7k5fo.cfg
Using config file "/etc/xen/g-ida7k5fo.cfg".
Error: Not enough free memory and enable-dom0-ballooning is False, so I cannot release any more. I need 2138112 KiB but only have 1930744.

so if i take the 16384mb of ram minus the used space and the space xen sys it still has i get:

16384 - 14037 - 1930744/1024 ~= 461.5mb

does the hypervisor really need 460mb of memory?
is there a way to calculate how much memory the hypervisior needs?

lg philipp

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