Xen users - Jan 2006 - Strange Xen arithmetic ("Error creating domain: I need 65 MiB, but dom0_min_mem is 196...")

I run Xen 3.0, dom0 is a Debian "sarge" with kernel 2.6.12.6. I can
start the first domU (I tried with several guests OS) but the second
always fail:

aslan:/etc/xen % sudo xm create gentoo-diggory.cfg -c
Using config file "gentoo-diggory.cfg".
Error: Error creating domain: I need 65 MiB, but dom0_min_mem is 196 and
shrinking to 196 MiB would leave only -85 MiB free.

The box has only 196 Mb of RAM. dom0 received 48 Mb (and I can check
with "free" that it is indeed the case). Each domU is configured for
64 Mb so I believe that 48 + 64 + 64 < 196. but Xen seems to think
otherwise and display this strange sentence above.

Any idea?


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Modify the dom0_min_mem entry in /etc/xen/xend-config.sxp to from 196 to 64.

Regards,

Anthony Liguori

Stephane Bortzmeyer wrote:
>I run Xen 3.0, dom0 is a Debian "sarge" with kernel 2.6.12.6. I
can
>start the first domU (I tried with several guests OS) but the second
>always fail:
>
>aslan:/etc/xen % sudo xm create gentoo-diggory.cfg -c
>Using config file "gentoo-diggory.cfg".
>Error: Error creating domain: I need 65 MiB, but dom0_min_mem is 196 and
shrinking to 196 MiB would leave only -85 MiB free.
>
>The box has only 196 Mb of RAM. dom0 received 48 Mb (and I can check
>with "free" that it is indeed the case). Each domU is configured
for
>64 Mb so I believe that 48 + 64 + 64 < 196. but Xen seems to think
>otherwise and display this strange sentence above.
>
>Any idea?
>
>
>_______________________________________________
>Xen-users mailing list
>Xen-users@lists.xensource.com
>http://lists.xensource.com/xen-users
>
>  
>

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On Mon, Jan 30, 2006 at 10:45:50PM -0600,
 Anthony Liguori <aliguori@us.ibm.com> wrote 
 a message of 37 lines which said:
> Modify the dom0_min_mem entry in /etc/xen/xend-config.sxp to from 196 to
64.
OK, tuning this parameter is not obvious (setting it too low has many
strange effects such as virtual machines hanging and even the host OS
freezing) but now, I have: 

(dom0-min-mem 16)

And I can run two domU and my dom0 in my 192 Mb of physical RAM:

aslan:~ % sudo xm list                
Name                              ID Mem(MiB) VCPUs State  Time(s)
Domain-0                           0       46     1 r-----   135.1
diggory                            2       64     1 ------    36.3
polly                              3       64     1 ------    32.3

Thanks a lot for pointing to that parameter.

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hi,

Anthony Liguori schrieb:
> Modify the dom0_min_mem entry in /etc/xen/xend-config.sxp to from 196 to
> 64.
i have a similar problem:

Using config file "/etc/xen/vhost1.sxp".
Error: I need 129 MiB, but dom0_min_mem is 48 and shrinking to 48 MiB
would leave only 44 MiB free.

i change the config from 48 to 129, so, do i have to restart the
complete server, or can i change it on the fly, while the domu''s
running?

cu denny


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