Xen devel - Apr 2006 - Small Memory Issue with Xm-Test

The recent move to the -xen kernel has made the small memory issue
resurface with xm-test. The 15_create_smallmem_pos.py will fail because
the 16 MBs it loads isn''t enough, the domain hangs with out of memory
issues. We can''t know, ahead of time, the minimal amount of memory that
will allow the domain to boot and work. Xm-Test needs to be adjusted to
work.

Should we?

1) Bump 15_create_smallmem_pos.py to 32 or 64 MBs? Is there a number
that seems reasonable? 

2) Bump the default memory for domains from 64 MBs to something larger?

We can certainly document the issue in xm-test and describe how to bump
memory should an issue occur.

This brings up handling the normal case of domain creation with regard
to small memory. It isn''t possible to know ahead of time how much
memory
will be needed by the created domain. We could:

1) Patch the xm create process to warn the user if a domain is created
with less than a certain memory amount like 32 or 64 MBs. 

2) Patch the default domain configs to contain a warning about using
small memory amounts and the possible repercussions. 

3) Patch documentation to outline the issue - such as the xm manpage and
the user manual.

Suggestions?

I can certainly create the patches. I would like to know what the
consensus is regarding what to do.

I''ve created bug 616 to track this issue:

http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=616

Thanks,

Dan


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DS> 1) Bump 15_create_smallmem_pos.py to 32 or 64 MBs? Is there a
DS> number that seems reasonable?

I think it''s still a valid test.  Perhaps xm should have a helpful
minimum (with the accompanying --force flag) to help the user not
shoot herself in the foot?  If so, then xm-test should verify that
this check works by trying to create a domain with a memory amount
below that limit.

DS> 1) Patch the xm create process to warn the user if a domain is
DS> created with less than a certain memory amount like 32 or 64 MBs.

Yes, I think this is reasonable.

Does anyone know of a metric we could use to determine the minimum
amount of memory required, perhaps my looking at the domU kernel?
This would be cool if it was reliable, but I think the minimum amount
is a reasonable solution.

-- 
Dan Smith
IBM Linux Technology Center
Open Hypervisor Team
email: danms@us.ibm.com


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