Xen users - Nov 2006 - How many VMs/domains can Xen run?

Hi :)

Is there any "known" limit to the number of VMs/domains you can run on
Xen?

I know this depends on the hardware you''ve got: RAM, CPU, ...
It''s just that
I''m interested in knowing if there''s a known limit.

TIA

   Rafa

-- 
50% of all statistics are inaccurate.

OpenWengo: rgriman

_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

> -----Original Message-----
> From: xen-users-bounces@lists.xensource.com 
> [mailto:xen-users-bounces@lists.xensource.com] On Behalf Of 
> Rafa Grimán
> Sent: 02 November 2006 14:47
> To: xen-users@lists.xensource.com
> Subject: [Xen-users] How many VMs/domains can Xen run?
> 
> Hi :)
> 
> Is there any "known" limit to the number of VMs/domains you 
> can run on Xen?
> 
> I know this depends on the hardware you''ve got: RAM, CPU, ... 
> It''s just that 
> I''m interested in knowing if there''s a known limit.
In a default build and without any changes to command-line, the heap that Xen
uses to allocat it''s internal data limits the number of domains to
around 100 in the 13 MB of heap that is default. It''s perfectly
possible to increase this by changing a constant in a header-file, but there are
some side effects (that I don''t quite remember what they are). In the
64-bit version(s) of Xen, you can even just throw on a command-line argument to
increase the heap, but not in 32-bit mode (because of said side-effects).

[Speculation: I believe the side-effects is that more space is occupied by
page-tables in each domain, so if you increase the size of the heap, each domain
will have to have extra page-table-entries to get to the large sized heap, and
thus each domain will in itself take up more space - but that''s just
what I think].

So, assuming we''d increased the size of the heap, the answer is really
"As many as you can fit in your memory"... And if they are small, that
could be quite a few!

--
Mats
> 
> TIA
> 
>    Rafa
> 
> -- 
> 50% of all statistics are inaccurate.
> 
> OpenWengo: rgriman
> 
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
> 
> 
> 


_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

On Thu, 2006-11-02 at 15:57 +0100, Petersson, Mats
wrote:
>  
> In a default build and without any changes to command-line, the heap that
Xen uses to allocat it''s internal
> data limits the number of domains to around 100 in the 13 MB of heap that
is default.
> It''s perfectly possible to increase this by changing a constant in
a header-file,
If interested in tinkering with it the header file is: 

[xen-src]/xen/include/asm/config.h , lines of interest are between 210 -
240 .. I tried decreasing it to cram and optimize Xen in small 2.6 based
systems and it seemed to work (kinda), haven''t done much with that
particular project since funding got pulled. 

The result was unstable, but we played with quite a bit more too, so I
can''t be certain adjusting it for x86_32 results in something unstable.

Keep in mind "asm" is going to be a symlink to whatever the target was
of your last build, use readlink to be sure :)

Best,
-Tim



_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users