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Re: [Xen-devel] Re: [Xen-changelog] fail domU creation if memory need co

To: Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [Xen-changelog] fail domU creation if memory need couldn't be succeed after ballooning out dom0
From: Anthony Liguori <aliguori@xxxxxxxxxx>
Date: Thu, 18 Aug 2005 10:51:22 -0500
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Ian Pratt wrote:

In general, we should try to avoid using timeouts at all cost. If we do have to use a timeout, then we should make sure it's long enough that the timeout is never going to happen. It's surprisingly easy to have enough load on your system such you miss a 2 second timeout.

Yep, in general I'm all for making timeouts long enough to be visible.

However, this timeout is different: its something we expect may fail (as
opposed to an internal failure of the tools).

Is it really possible to fail?  I just did:

echo 42 > /proc/xen/balloon

On domain-0 and the system crashed. It would be nice if it actually failed but currently the only thing this timeout will do is prevent us from working when we could have :-)

How about when we fix the balloon driver, we have it write a node in the store that indicates whether the balloon has succeeded or failed and then the tools can simply set a watch and wait for something to happen?


Anthony Liguori

We're asking domain 0 to
try and shrink itself. It may be unable to, in which case trying for a
few seconds and then failing the domain create seems like a good
approach. If domain 0 can't page enough stuff out after a second or two,
its unlikely to succeed without operator intervention (e.g. killing

2s is perhaps overly short, but I doubt going larger than 5s would
result in any greater chance of success, and would just anoy users.


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