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

[Alain BARTHE <alain.barthe@xxxxxxxx>]

xen-users-bounces@xxxxxxxxxxxxxxxxxxx a écrit sur
21/01/2008 15:30:31 :

> 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...

Reading the documentation, Xen does have ballooning.
Without the dom0_mem parameter, the dom0 uses all available memory, then
it "balloons out" enough memory for each created domU, until
it reaches the minimum amount of memory for itself, defined in the "dom0-min-mem"
parameter of the xend-config.sxp file. In this case, it refuses to ceate
the domU.
Nowhere the documentation talks about a "balloon
in" of the memory when a domU is stopped. IMHO, this behavior is understandable.

If you really want to release to the dom0 the memory
used by the stopped domU, try to do this manually by:
        xm mem-set 0 2G

Greetings,
Alain

> 
> 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
> 
> _______________________________________________
> Xen-users mailing list
> Xen-users@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-users
> 
> !DSPAM:87,47949d08307143761620701!
> 
> 
> 
> 
> _______________________________________________
> Xen-users mailing list
> Xen-users@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-users
_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users