Re: [Xen-devel] Handling of out of memory conditions (was: Re: Strange kernel BUG() on PV DomU boot)

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Fri, Jun 22, 2012 at 1:53 PM, Joanna Rutkowska
<joanna@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>>> > Any recommendations regarding the preferred minimum Xen free memory, as
>>> > reported by xl info, that should be preserved in order to assure Xen
>>> > runs smoothly?
>> In pre-4.2 Xen, there's not much you can do when memory gets
>> fragmented (otherwise you'd have to keep more than half the
>> memory in the box in the hypervisor). With multi-page runtime
>> allocations gone, you should be fine leaving just a minimal amount
>> to the hypervisor.
>
> Right, but 4.2 will not be released until weeks or months :/ And we
> would like to release Qubes 1.0 within weeks...

FWIW, XenServer has had to tackle this same issue.  As I understand
it, what they ended up doing was to have a model of how much memory
they thought each VM was going to use (based on things like guest
memory, video ram size, number of vcpus, and so on).  They then
manually try to track how much memory they think each running VM was
using, and used that to figure out whether they would be able to start
a new VM or not.  Obviously that's a big pain to set up and keep
current; but it has actually seems to work tolerably well for them.

The XenServer toolstack is open source, so it shouldn't be a problem
to share that formula.  If you think that would work for you, I think
Jonathan Ludlam is probably the guy to help out with that.

 -George

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