Re: [Xen-devel] Memory allocation going seriously wonky on 4.1.1

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Oct 03, 2011 at 02:45:36PM +0100, Anthony Wright wrote:
> On 01/10/2011 13:07, Pasi Kärkkäinen wrote:
> > On Fri, Sep 30, 2011 at 04:07:06PM +0100, Anthony Wright wrote:
> >> I have a machine with 16GB of RAM running 32 bit xen 4.1.1 with Dom0
> >> running a 3.0.4 linux kernel and 23 paravirtualized DomUs.
> >>
> > Hey,
> >
> > Why 32bit Xen? I think all (most?) hypervisor testing happens with 64bit 
> > Xen.
> > Note that you can still have 32bit dom0 kernel with 64b hypervisor.
> I'm going to investigate 64 bit xen on a 32 bit Dom0 soon, but as to the
> 32 xen, I work quite a lot with older hardware and Xen since it does
> paravirtualisation, and it's a really good way to re-use old hardware.
> >> As the free ram gets to 2391 MB free the system behaves as if it's got
> >> no more ram, and starts grabbing ram from Dom0, before getting even more
> >> confused and failing to start DomUs and eventually crashing the whole
> >> machine. I have attached a tarball with the output of xl dmesg, xl info
> >> & xl list at various points.
> >>
> > - Do you use dom0_mem= parameter for Xen? 
> > - Did you disable dom0 ballooning? 
> >
> > http://wiki.xen.org/xenwiki/XenBestPractices
> I was already using the dom0_mem= parameter on the xen hypervisor, but I
> disabled dom0 ballooning (enable-dom0-ballooning no), and just for good
> measure I also set (dom0-min-mem 2000). This had no effect, when I
> increase the 10-4 memory requirements, on restart the Dom0 memory is
> reduced to 1713MB and xl info reports 2391MB free.
> >> Stage 1
> >> Everything is fine, Dom0 has 2000MB according to xl list, and 'xl info'
> >> says there is 2405MB free.
> > - How much memory did dom0 initially have? 
> > - Did you use mem= parameter for dom0 kernel (vmlinuz) ?
> >
> > See: http://wiki.xen.org/xenwiki/Linux_30_bugs
> dom0 starts with 2000MB.
> I didn't use mem= on the linux kernel - I thought it wasn't neccessary.

It is if your kernel does not have these two patches:

    xen: use maximum reservation to limit amount of usable RAM
    xen/e820: if there is no dom0_mem=, don't tweak extra_pages.

.. oh and you also need to update the hypervisor to include:
"
    For dom0, this requires at patch to Xen ('x86: use 'dom0_mem' to limit
    the number of pages for dom0') (c/s 23790)
"

Grrr.. Let me update the 3.0 bug-list

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