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RE: [Xen-users] Set memory free after shutdown

To: "'Daniele Piaggesi'" <d.piaggesi@xxxxxxxxxxxx>, <deshantm@xxxxxxxxx>
Subject: RE: [Xen-users] Set memory free after shutdown
From: "Jeroen Torrekens" <jeroen.torrekens@xxxxxxxxxxx>
Date: Mon, 21 Jan 2008 15:30:31 +0100 (CET)
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Well... Let's suppose you give the 1GB of memory the VM was consuming back
to the dom0. It starts it and filling it up. What do you think will happen
if you want to start the VM again? He will tell you he doesn't has enough
free memory to boot your VM. I think Xen doens't have something like
ballooning (it starts a dummy process which comsumes lots of memory to
make the machine put his own processes into swap to free the physical
memory to launch the VM). That's why it is best to put the dom0_mem
parameter in the kernel line...

Greetings,
Jeroen

-----Original Message-----
From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Daniele
Piaggesi
Sent: maandag 21 januari 2008 14:24
To: deshantm@xxxxxxxxx
Cc: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Set memory free after shutdown



Todd Deshane wrote:
> You should look into the dom0_mem Xen boot option to adjust this.
>
http://tx.downloads.xensource.com/downloads/docs/user/#SECTION041300000000
00000000
> 
> It seems that dom0 could then reclaim up to that (dom0_mem) maximum 
> amount of memory freed by VMs.

First of all thanks for help. Anyway I think that my problem should be a 
bit different. I notice that if I have a physical machine with (for 
example) 4Gb of Ram, and I start 3 virtual machine each one with 1Gb of 
Ram, the dom0 results to have the remaining free memory, that is 1Gb. So 
far so good. But if I stop one virtual machine (then the virtual 
machines used memory decrease to only 2Gb), dom0 still results to have 
only 1Gb. Then I think: Where is the giga released? And above all: why 
the memory released don't increase automatically, the dom0 memory (that 
is the physical host memory)? Is there a way to adjust this?

I don't know if my analysis is correct or if there's another way, or I'm 
doing something wrong, 'cause I'm not very expert about Xen, but I would 
to release to dom0, the memory previously used for one vm now stopped.

Thanks :)
Daniele

-- 
Daniele Piaggesi
Linux System Administrator
--------------------------
(Pro-Netics) S.p.A.
Sourcesense - making sense of OpenSource
http://www.pronetics.it
Via E. L. Cerva 127/C
00142 Roma - Italy
Tel (+39) 0651530849
Mob (+39) 3286176226

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