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Re: [Xen-devel] [PATCH] Add Small Memory Warning to XM for create and me

To: Anthony Liguori <aliguori@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Add Small Memory Warning to XM for create and mem-set
From: Ewan Mellor <ewan@xxxxxxxxxxxxx>
Date: Mon, 24 Apr 2006 01:55:11 +0100
Cc: Daniel Stekloff <dsteklof@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Mark Williamson <mark.williamson@xxxxxxxxxxxx>
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On Fri, Apr 21, 2006 at 05:41:34PM -0500, Anthony Liguori wrote:

> Mark Williamson wrote:
> >I really like this idea.  I think it's most important for ballooning, 
> >which is a really easy way to get a domain to commit suicide otherwise ;-)
> >
> >I'd quite like to see it implemented Xend-side, though, with the "warning 
> >level" configurable (and probably disablable) in the xend-config.sxp so 
> >that users who really do want to create very small domUs can tweak the 
> >system not to warn them.
> >  
> I'm not sure I agree that Xend is the right place to do this.  You would 
> have to add another parameter to the either the domain config or to the 
> actual create() call that basically had the semantics of "if memory is 
> less than X, throw an exception."  That seems like a rather awkward 
> addition to the interface and it makes client code harder to write.
> I'll attempt to be telepathic here and guess that you suggested this 
> because there's no xm config file so there's no easy way to be able to 
> tell xm to never give an error when mem is too small?  I think this is a 
> good point in time to start thinking about just implementing an xm 
> config file.
> If you use SafeConfigParser and just grab from a standard location (say 
> /etc/xen/xm.conf), you should be able to do it properly (just within xm) 
> with very little code.

I agree.  Daniel, could you redo your patch, introducing an xm config file
rather than a --force-mem option?  If you could make it so that xm works even
without the config file, using some decent defaults, that would avoid breaking
existing installations, which would be good.

Personally, I'd have an XML-based config file rather than a win.ini style one
-- we're moving towards using XML everywhere else, so it makes sense to me.
Anyone have any strong opinions here?


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