View Full Version : Calculating memory used by Xen hypervisor

21-Oct-2011, 22:46
According to 'TID 3559698 - XEN Dom0 becomes unresponsive when shutting
down a domU virtual machine'
I should be able to calculate approximately how much memory is
used/needed by the Xen hypervisor.> it is possible to get a good idea of how much is required by booting XEN
> in the default configuration (all available memory assigned to dom0).
> In this configuration, the total system memory minus the amount of
> memory assigned to dom0 equals the amount required by the hypervisor.
With -only Dom0 running-, I see:

server:~ # xm info
host : server
release :
version : #1 SMP 2011-08-22 10:12:58 +0200
machine : x86_64
total_memory : 6143
free_memory : 3592
max_free_memory : 5557
max_para_memory : 5553
max_hvm_memory : 5532

According to the TID> The amount of memory needed by the hypervisor, domain0, and each domU
> varies based on machine specifications, type of VM, etc. Therefore,
> there are no fixed values that can be assigned to any of those
> variables. However, 'xm info' can provide a view into the current state
> of the system. There are 5 fields in the list that provide information
> about the memory status:
> total_memory : 6143 # Total RAM available to the system
> free_memory : 3592 # Free RAM (not in use by hypervisor, dom0, or any
> domU)
> max_free_memory : 5557 # Maximum value possible for"free_memory" after
> ballooning dom0
> max_para_memory : 5553 # Maximum amount of memory that could be
> assigned to a new pv guest
> max_hvm_memory : 5532 # Maximum amount of memory that could be assigned
> to a new fv guest
Dom0 has 2477 MB of memory assigned as can be seen here:

server:~ # xm list -l Domain-0
(domid 0)
(cpu_weight 256)
(cpu_cap 0)
(pool_name Pool-0)
(bootloader )
(vcpus 4)
(cpus ((0 1 2 3) (0 1 2 3) (0 1 2 3) (0 1 2 3)))
(on_poweroff destroy)
(description )
(on_crash restart)
(uuid 00000000-0000-0000-0000-000000000000)
(bootloader_args )
(name Domain-0)
(on_reboot restart)
(maxmem 16777215)
*(memory 2477)*
(shadow_memory 0)
(features )
(on_xend_start ignore)
(on_xend_stop ignore)
(cpu_time 147464.486225)
(online_vcpus 4)
(image (linux (kernel ) (superpages 0) (nomigrate 0) (tsc_mode 0)))
(status 2)
(state r-----)

I find it difficult to believe that the hypervisor is only using 74
6143-2477-3592 = 74 MB

The TID suggests that I need to make -all memory- available to Dom0 for
this calculation to work. I don't know where the 2477 MB limit is set
and I don't see how I can change the Dom0 settings as I would for a

Any ideas?

Kevin Boyle
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26-Oct-2011, 18:23

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