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Re: [Xen-devel] xl vs. xm: memory consumption

To: Christoph Egger <Christoph.Egger@xxxxxxx>
Subject: Re: [Xen-devel] xl vs. xm: memory consumption
From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Date: Tue, 9 Nov 2010 18:39:55 +0000
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On Fri, 5 Nov 2010, Christoph Egger wrote:
> Hi!
> Is it possible that xl needs more memory than xm?
> Does xl log somewhere how much memory is free and how much it does want?
> xl create -c <guest.conf>
> Parsing config file <guest.conf>
> failed to free memory for the domain
> xm create -c <guest.conf>
> [guest boot messages]

That's because of freemem-slack: a basic amount of memory left free
on the system otherwise memory allocation for new VMs fails.
It is calculated using the amount of free memory at boot time, assuming
that dom0 was booted using all the memory in the system.
If you boot dom0 passing dom0_mem to xen, then you have to disable
autoballooning (autoballoon=0 in /etc/xen/xl.conf).
Given the other bug you reported on libxl__fill_dom0_memory_info, I
suspect that the freemem-slack value might be wrong on your system.
On the other hand if your configuration is correct, we might have to
lower the maximum value of freemem-slack that currently is 15% of the
total memory in the system.

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