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Re: [Xen-devel] [PATCH] Disallow setting maxmem to higher value than tot

To: Michal Novotny <minovotn@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] Disallow setting maxmem to higher value than total physical memory size
From: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
Date: Wed, 1 Sep 2010 13:44:09 +0100
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On Wed, 2010-09-01 at 13:31 +0100, Michal Novotny wrote:
> Hi,
> this is the patch to disallow changing the maxmem value to higher value 
> than total physical memory size since without this patch I was able to 
> set dom0 maxmem to higher (invalid) value which is not correct.

I think it is allowable for a domU though. Consider the scenario where
you have two hosts, one of which has more physical RAM than the other.
You may which to boot a domain on the smaller host, (i.e. booting
ballooned with a current_pages suitable for the small host) and then
migrate it to the large machine where you then want to be able to
balloon to a value larger than was even possible on the previous

If maxmem is not configured to the largest amount you consider you might
want to give the domain then this scenario fails but it should work.

What is the actual issue with setting a larger maxmem even for domain 0
that you are trying to resolve? Just that it will continue to attempt to
balloon up and never get there?


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