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[Xen-devel] Xen balloon driver discuss

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Subject: [Xen-devel] Xen balloon driver discuss
From: tinnycloud <tinnycloud@xxxxxxxxxxx>
Date: Sun, 21 Nov 2010 14:26:01 +0800
Cc: George.Dunlap@xxxxxxxxxxxxx, dan.magenheimer@xxxxxxxxxx
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Thread-index: AcuJLGxgsHp7IzXJTWWvKqB8syu+nAAEyJ1Q
        Greeting first.

        I was trying to run about 24 HVMS (currently only Linux, later will
involve Windows) on one physical server with 24GB memory, 16CPUs.
        Each VM is configured with 2GB memory, and I reserved 8GB memory for
        For safety reason, only domain U's memory is allowed to balloon.
        Inside domain U, I used xenballooned provide by xensource,
periodically write /proc/meminfo into xenstore in dom
        And in domain 0, I wrote a python script to read the meminfo, like
xen provided strategy, use Committed_AS to calculate the domain U balloon
        The time interval is 1 seconds.

        Inside each VM, I setup a apache server for test.       Well, I'd
like to say the result is not so good.
        It appears that too much read/write on xenstore, when I give some of
the stress(by using ab) to guest domains, 
        the CPU usage of xenstore is up to 100%. Thus the monitor running in
dom0 also response quite slowly.
        Also, in ab test, the Committed_AS grows very fast, reach to maxmem
in short time, but in fact the only a small amount
        of memory guest really need, so I guess there should be some more to
be taken into consideration for ballooning.

        For xenstore issue, I first plan to wrote a C program inside domain
U to replace xenballoond to see whether the situation
        will be refined. If not, how about set up event channel directly for
domU and dom0, would it be faster?

        Regards balloon strategy, I would do like this, when there are
enough memory , just fulfill the guest balloon request, and when shortage 
        of memory, distribute memory evenly on the guests those request
        Does anyone have better suggestion, thanks in advance.

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