Xen devel - Apr 2006 - [PATCH] Add Small Memory Warning to XM for create and mem-set

Hi,

This patch adds a warning to xm for creating and setting a domain''s
memory under 32 MBs. Patch adds a "--force-mem" option to "xm
create"
and "xm mem-set" commands for creating or setting memory less than 32
MBs. Patch also updates man page and user manual.

All comments welcome.

Thanks,

Dan


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On Fri, Apr 21, 2006 at 08:17:38AM -0700, Daniel Stekloff wrote:
> 
> Hi,
> 
> This patch adds a warning to xm for creating and setting a
domain''s
> memory under 32 MBs. Patch adds a "--force-mem" option to
"xm create"
> and "xm mem-set" commands for creating or setting memory less
than 32
> MBs. Patch also updates man page and user manual.
> 
> All comments welcome.
You''ll need to patch 16_create_smallmem_neg, too, otherwise that test
will
fail.

Ewan.

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I really like this idea.  I think it''s most important for ballooning,
which is
a really easy way to get a domain to commit suicide otherwise ;-)

I''d quite like to see it implemented Xend-side, though, with the
"warning
level" configurable (and probably disablable) in the xend-config.sxp so
that
users who really do want to create very small domUs can tweak the system not 
to warn them.

Cheers,
Mark

On Friday 21 April 2006 16:17, Daniel Stekloff wrote:
> Hi,
>
> This patch adds a warning to xm for creating and setting a
domain''s
> memory under 32 MBs. Patch adds a "--force-mem" option to
"xm create"
> and "xm mem-set" commands for creating or setting memory less
than 32
> MBs. Patch also updates man page and user manual.
>
> All comments welcome.
>
> Thanks,
>
> Dan
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On Fri, 2006-04-21 at 16:29 +0100, Mark Williamson
wrote:
> I really like this idea.  I think it''s most important for
ballooning, which is
> a really easy way to get a domain to commit suicide otherwise ;-)
> 
> I''d quite like to see it implemented Xend-side, though, with the
"warning
> level" configurable (and probably disablable) in the xend-config.sxp
so that
> users who really do want to create very small domUs can tweak the system
not
> to warn them.

Ok, that makes sense. I will also try and remember to patch xm-test. 

Thanks,

Dan


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Mark Williamson wrote:
> I really like this idea.  I think it''s most important for
ballooning, which is
> a really easy way to get a domain to commit suicide otherwise ;-)
>
> I''d quite like to see it implemented Xend-side, though, with the
"warning
> level" configurable (and probably disablable) in the xend-config.sxp
so that
> users who really do want to create very small domUs can tweak the system
not
> to warn them.
>   
I''m not sure I agree that Xend is the right place to do this.  You
would
have to add another parameter to the either the domain config or to the 
actual create() call that basically had the semantics of "if memory is 
less than X, throw an exception."  That seems like a rather awkward 
addition to the interface and it makes client code harder to write.

I''ll attempt to be telepathic here and guess that you suggested this 
because there''s no xm config file so there''s no easy way to be
able to
tell xm to never give an error when mem is too small?  I think this is a 
good point in time to start thinking about just implementing an xm 
config file.

If you use SafeConfigParser and just grab from a standard location (say 
/etc/xen/xm.conf), you should be able to do it properly (just within xm) 
with very little code.

Thoughts?

Regards,

Anthony Liguori
> Cheers,
> Mark
>
> On Friday 21 April 2006 16:17, Daniel Stekloff wrote:
>   
>> Hi,
>>
>> This patch adds a warning to xm for creating and setting a
domain''s
>> memory under 32 MBs. Patch adds a "--force-mem" option to
"xm create"
>> and "xm mem-set" commands for creating or setting memory less
than 32
>> MBs. Patch also updates man page and user manual.
>>
>> All comments welcome.
>>
>> Thanks,
>>
>> Dan
>>     
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
>   

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AL> I''m not sure I agree that Xend is the right place to do this. 
You
AL> would have to add another parameter to the either the domain
AL> config or to the actual create() call that basically had the
AL> semantics of "if memory is less than X, throw an exception." 
That
AL> seems like a rather awkward addition to the interface and it makes
AL> client code harder to write.

I agree.

AL> Thoughts?

I think it''s a good idea.  I''d rather see it in the client
than in
Xend.  If some GUI app wants to have a configurable limit that''s easy
for the user to access, then it''ll just end up minding the limit
itself, and call create() with the force flag each time, which defeats
the point anyway.

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


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On Fri, Apr 21, 2006 at 05:41:34PM -0500, Anthony Liguori wrote:
> Mark Williamson wrote:
> >I really like this idea.  I think it''s most important for
ballooning,
> >which is a really easy way to get a domain to commit suicide otherwise
;-)
> >
> >I''d quite like to see it implemented Xend-side, though, with
the "warning
> >level" configurable (and probably disablable) in the
xend-config.sxp so
> >that users who really do want to create very small domUs can tweak the 
> >system not to warn them.
> >  
> 
> I''m not sure I agree that Xend is the right place to do this.  You
would
> have to add another parameter to the either the domain config or to the 
> actual create() call that basically had the semantics of "if memory is
> less than X, throw an exception."  That seems like a rather awkward 
> addition to the interface and it makes client code harder to write.
> 
> I''ll attempt to be telepathic here and guess that you suggested
this
> because there''s no xm config file so there''s no easy way
to be able to
> tell xm to never give an error when mem is too small?  I think this is a 
> good point in time to start thinking about just implementing an xm 
> config file.
> 
> If you use SafeConfigParser and just grab from a standard location (say 
> /etc/xen/xm.conf), you should be able to do it properly (just within xm) 
> with very little code.
I agree.  Daniel, could you redo your patch, introducing an xm config file
rather than a --force-mem option?  If you could make it so that xm works even
without the config file, using some decent defaults, that would avoid breaking
existing installations, which would be good.

Personally, I''d have an XML-based config file rather than a win.ini
style one
-- we''re moving towards using XML everywhere else, so it makes sense to
me.
Anyone have any strong opinions here?

Ewan.

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> I''m not sure I agree that Xend is the right place to do this.  You
would
> have to add another parameter to the either the domain config or to the
> actual create() call that basically had the semantics of "if memory is
> less than X, throw an exception."  That seems like a rather awkward
> addition to the interface and it makes client code harder to write.
Surely there are already plenty of other cases in which Xend can fail a create 
and throw the result back to xm?  For instance, if the kernel image
can''t be
found, hotplug scripts fail, etc.  Wouldn''t it just be an extra case of
that?
> I''ll attempt to be telepathic here and guess that you suggested
this
> because there''s no xm config file so there''s no easy way
to be able to
> tell xm to never give an error when mem is too small?  I think this is a
> good point in time to start thinking about just implementing an xm
> config file.
Well, yes and no.

Yes, Xend is the only place to do this right now.  But we''ve always
tried
(modulo a few things, eg pygrub) to keep xm a pretty thin layer, with most of 
the real smarts in Xend.  This also makes it easier to create a 
network-transparent implementation of xm, without confusing Xen-related 
config files on the "control" machine and on the servers.

That said, warning about improper config choices does seem rather like a 
client-side operation so perhaps an xm.conf is worth considering.

We should also consider:
1) whether we''re going to need this for other options (I suspect yes,
but it''d
be unfortunate to have a config file for just one option)
2) whether there are any config choices currently handled by Xend or the 
domain config files, which we''d rather be handled by xm.conf
> If you use SafeConfigParser and just grab from a standard location (say
> /etc/xen/xm.conf), you should be able to do it properly (just within xm)
> with very little code.
Agreed, should be a fairly simple little hack.

Cheers,
Mark
> Thoughts?
>
> Regards,
>
> Anthony Liguori
>
> > Cheers,
> > Mark
> >
> > On Friday 21 April 2006 16:17, Daniel Stekloff wrote:
> >> Hi,
> >>
> >> This patch adds a warning to xm for creating and setting a
domain''s
> >> memory under 32 MBs. Patch adds a "--force-mem" option
to "xm create"
> >> and "xm mem-set" commands for creating or setting memory
less than 32
> >> MBs. Patch also updates man page and user manual.
> >>
> >> All comments welcome.
> >>
> >> Thanks,
> >>
> >> Dan
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@lists.xensource.com
> > http://lists.xensource.com/xen-devel
-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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