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RE: [Xen-users] Is there a limit on the number of guest domains ?

  • To: "Ralph Passgang" <ralph@xxxxxxxxxxxxx>, <xen-users@xxxxxxxxxxxxxxxxxxx>
  • From: "Puthiyaparambil, Aravindh" <aravindh.puthiyaparambil@xxxxxxxxxx>
  • Date: Wed, 8 Feb 2006 12:12:32 -0500
  • Delivery-date: Wed, 08 Feb 2006 17:23:58 +0000
  • List-id: Xen user discussion <xen-users.lists.xensource.com>
  • Thread-index: AcYs0tjfA0M8/UuvT7q8Yfw3XSYOMg==
  • Thread-topic: [Xen-users] Is there a limit on the number of guest domains ?

> Am Mittwoch, 8. Februar 2006 17:33 schrieb Puthiyaparambil, Aravindh:
> > We did a few scalability tests on x86_64 Xen and found that the
> > limit on DomUs is 87. This is of course on a system that has enough
> > system memory to support that many DomUs as Xen does not over-commit
> > memory. In our tests each DomU had 64MB of RAM.
> interessting... but what happend after domU no. 87? what message/error
> you
> saw then? how much memory had your x86_64 testsystem? on wich xen
> have you made these tests?

The test was done on a 32x ES7000 with 8GB memory.

We started 87 SLES9 "minimum" DomUs with 64MB of RAM. Xentop reported 6
GB used, but we got an "out of memory error" when we tried to start the
88th. This happened even when more memory was given to Dom0.

> i would like to understand why there is such a limit...

It has something to do with the way heap allocation is done in Xen. If
the heap allocation is made dynamic then this limit would go away. But
from what Kier told me, it is a big change and we should hold off on
this for the moment.


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