Re: [Xen-users] 'xl reboot domid' ignores all in-memory changes AND the domu's config file changes

[msd+xen-users@xxxxxx]

Hello !

First, thank you very much for your help ! :)

a. What I want to do
--------------------

1. In the Dom-0, reduce the memory of one Dom-U "domu1" from 2048 to 1024
2. Create a new Dom-U "domu2" with 1024 Mb of memory
3. When the Dom-U "domu1" want to reboot (a kernel update for example), 
it keeps 1024 Mo of memory and not 2048, because it will crash !
For doing this :
- In the Dom-0, I use 'xl mem-set domu1 1024' and I change the memory 
value from 2048 to 1024 in the file '/etc/xen/dumu1.cfg'
- I create a new file '/etc/xen/dumu2.cfg' with 1024 Mb of memory and I 
use 'xl create /etc/xen/domu2.cfg'
If I use 'xl li', I can see that my 2 Dom-U have 1024 Mb of memory.

But, when, one day, the domu1 wants to reboot, it crashes because there 
is not enouth memory in the xen memory pool because it wants 2048 
instead of 1024.
So, is it possible to :
- when domu1 reboot, destroy the machine and recreate the machine with 
it's updated conf file '/etc/xen/dumu1.cfg' ?
- or, when domu1 reboot use the value of mem-set (or the mem-max value) 
as a parameter for the new virtual machine for domu1 ?
If no, do you have a solution for this problem ?

b. mem-max
----------

Austin S. Hemmelgarn <ahferroin7@xxxxxxxxx> wrote :
> xl mem-max is what you're thinking of probably, it lets you adjust 
the max-mem value dynamically, although the OS has to have hotplug 
support in the Xen balloon driver (I think most Linux distros do, but 
I'm not certain as I run custom kernels for all my Linux VM's). Unlike 
the regular xl mem-set command, this will persist through an xl reboot.
I have tried to play with mem-max, but it is the same problem. Even if I 
reduce the mem-max to 1024, when the dom-u restart, it take back 2048 Mb 
of RAM.
c. Documentation
----------------

I've seen in the xl documentation the 'config-update' parameter 
(http://xenbits.xen.org/docs/4.4-testing/man/xl.1.html).
> Update the saved configuration for a running domain. This has no 
immediate effect but will be applied when the guest is next restarted. 
*This command is useful to ensure that runtime modifications made to the 
guest will be preserved when the guest is restarted.*
1. So I understand there is a way to ensure runtime modification to a 
guest can be preserved when the guest is restarted, no ?
2. When I try this command (xl config-update domu1 /etc/xen/domu1.cfg) I 
have a "Erreur de segmentation" (may be "segfault error" in English). Why ?

Thank you in advance for your replies,

Regards,


Msd

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