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

[Pasi Kärkkäinen <pasik@xxxxxx>]

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.

> 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


> 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


> Stage 2
> I have increased the memory for the DomU labelled 10-4 from 700MB to
> 1000MB, Dom0 has 1713MB and 'xl info' says there is 2391MB free.
> 
> Stage 3
> I have tried to increase the memory for the DomU labelled 13-4 from
> 700MB to 1000MB, but it failed on the 'xl create' displaying the message
> 'failed to free memory for the domain'. Dom0 has 1413MB and 'xl info'
> says there is 3391MB free.
> 
> State 4
> I tried to create the 13-4 DomU again, and this time it succeeds. Dom0
> has 1413MB and 'xl info' says there is 2391MB free.
> 
> If I repeatedly stop and start DomUs at this point, particularly if I
> request more ram, the machine locks up. This may be due to lack of Dom0 ram.


-- Pasi


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