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[Xen-devel] out-of-memory problem when restoring ballooned domains

To: xen-devel <Xen-devel@xxxxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] out-of-memory problem when restoring ballooned domains
From: Lars Rasmusson <Lars.Rasmusson@xxxxxx>
Date: Thu, 10 Mar 2005 10:42:53 -0800
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I have a problem with the balloon functionality.

I have a 2G memory machine (with 2 CPUs).

I want to create three (or more) user domains, 
each configured to have 2G (or 1800MB) of RAM,
but ballooned down to 128 MB.

The reason is that I want to be able to change the
size of the balloons during run time, and I want
each of the domains to be able to potentially get
all (or almost all) of the memory.

I first create the domains t1, t2, and t3:

xm create t1 memory=1800
xm balloon t1 128
# wait until the balloon is inflated
xm save t1 t1.saved

and repeat for t2 and t3.  Notice that I can
create the domains with maximum memory since
the other domains are not using any RAM at
the time.

Here comes my problem:

When I do 

xm restore t1.saved
xm restore t2.saved
xm restore t3.saved

I get "Error: 1" when I create the third
domain.  I get the feeling it has something to
do with "not enough memory" (is that  correct?)

So even though the three 128 Mb domains should
fit easily within the approx 2G RAM, Xen doesn't 
think so.  Which is why I've come to think there 
might be some problem with how it is counting available RAM.

- Is Xen taking ballooned memory into account properly?

- Is it interpreting the info in the .saved file correctly?

If that is the bug, I then wonder why I'm able to get two 
user domains up and running, and not just one...  
Could that be related to that the machine is a 2 CPU machine?

Well that's just speculation... Does anyone have any
suggestions what I might be doing wrong, or where the 
problem may be?

Lars Rasmusson

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