[xenpreview-dev] default dom0 memory size comsumes almost all memory available on system

[Charles Coffing]

When you attempt to create a domain, xend will automatically scale down
domain 0's memory usage as needed, down to the minimum amount specified
in /etc/xen/xend-config.sxp (look for the 'dom0-min-mem' setting.)  This
happens automatically and transparently, whether you are working through
YaST, or the 'xm' command, or via CIM, since the request will ultimately
be handled by xend.

Currently, this works fine for paravirtualized; full virtualization
doesn't quite balloon down enough (so in that case, you do currently
have to manually mem-set first.)  This is a bug we're working on.

I do imagine that larger deployments will specify a value in grub, but
auto-ballooning in domain 0 seems best as the default.  This makes it
easier to get started with Xen.

-Chuck

>>> On Thu, Mar 16, 2006 at  8:05 AM, in message
<EF8D308BE33AF54D8934DF26520252D303504170 at USTR-EXCH5.na.uis.unisys.com>,
"Krysan, Susan" <KRYSANS at unisys.com> wrote: 
> I would like to start a discussion concerning the default memory size

> allocated to dom0 in the version of Xen bundled with SLES10.  I do
not 
> specify a dom0 memory size in /boot/grub/menu.lst, nor do I set a
size using 
> xm mem- set or xm max- mem.  No matter what amount of memory is
available on the 
> box, dom0 is allocated almost all of the memory by default.  For
example, on 
> an 8 GB box, only about 132 MB is left free for booting domUs.  This

> surprised me.  In an enterprise server environment, it is most likely
that 
> users will be using Xen either to boot many small memory size domUs
or even 
> just one or two larger ones.  With only 132 MB available on an 8 GB
system, 
> this means that a user would get insufficient memory errors when
trying to 
> boot domUs if he did not remember to configure the size of dom0. 
Wouldn't it 
> be more user friendly to have a default memory size for dom0 which is
smaller 
> but large enough for dom0 to run efficiently, perhaps 512 MB, and
allow most 
> of the memory on the box to be free for booting domUs, since the
purpose of 
> booting Xen is to run domUs?
> 
> Thanks,
> 
> Sue Krysan
> Linux Systems Group
> Unisys Corporation
> 
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