Re: [Xen-users] Memory squeeze in netback driver?

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> > I've not tried setting dom0_min_mem, this is also a kernel param?
> > Any suggestions on what that size should be?
>
> It's a setting in /etc/xen/xend-config.sxp.  Set it to something reasonable
> to make sure that dom0 doesn't get ballooned down too far.  I think for a
> production machine a sensible measure would be to set dom0-min-mem=0 to
> disable auto-ballooning entirely - then set dom0_mem on the Xen command
> line.
>
> On my test box where I run up to about 3-4 domUs, not heavily loaded, I
> have been running with dom0-min-mem=196M and dom0_mem=256M.  I should
> probably just disable ballooning altogether on this machine.
>
> A static dom0 memory allocation should really be just fine on a server, the
> auto-ballooning is more useful for desktop use or for playing around and
> getting the feel of things without having to reconfigure manually all the
> time.

I'd just like to add at this point that I suspect it's possible that 
ballooning dom0 to too small a size *or* setting dom0_mem to too small a size 
could cause memory squeezes.

But also, they have been known to occur in the past by dom0 being ballooned 
down by too many MB when the Linux memory manager confuses the ballooning 
with memory pressure - even though dom0 still ought to have enough memory 
free.  I'm not sure if this can still happen, but this is why I recommend 
using a static allocation on a production server.

Cheers,
Mark

> Cheers,
> Mark
>
> > --jason
> >
> > On May 3, 2007, at 4:03 PM, Ryan Burke wrote:
> > >> Is there any rule for how much memory dom0_mem should be set to?
> > >> I've got 16g in this machine, and run ~12 1g domU's.
> > >>
> > >> Is more memory for dom0_mem better?  or is less better?
> > >>
> > >> --jason
> > >>
> > >> On May 3, 2007, at 8:14 AM, Adam Jacob wrote:
> > >>> On Thu, May 03, 2007 at 03:03:43AM -0700, Jason Dillon wrote:
> > >>>> I've been running into this from time to time... usually when xm
> > >>>> creating a new domU, /var/log/messages for dom0 spits out:
> > >>>>
> > >>>> <snip>
> > >>>> May  3 02:56:04 tweak kernel: printk: 4 messages suppressed.
> > >>>> May  3 02:56:04 tweak kernel: xen_net: Memory squeeze in netback
> > >>>> driver.
> > >>>> </snip>
> > >>>>
> > >>>> And at this point all of the network connectivity for *all* domU's
> > >>>> controlled for that dom0 vanish.  I have to xm shutdown and xm
> > >>>> create
> > >>>> them again to get the network back.  This doesn't happen all of the
> > >>>> time, seems rather random really.
> > >>>>
> > >>>> Its *really* annoying.  Is there a way to prevent this from
> > >>>> happening?
> > >>>
> > >>> You need to set the dom0_mem parameter at boot time.  Something
> > >>> like:
> > >>>
> > >>> kernel          /xen-3.0.3-1-amd64.gz dom0_mem=256M
> > >>>
> > >>> Has been working for us.
> > >>>
> > >>> Adam
> > >
> > > Have any of you tried setting the dom0_min_mem variable? I had this
> > > problem back in 3.0.2 and if I remember right the solution was to set
> > > dom0_min_mem so that there wasa minimum that Dom0 would balloon
> > > down. I
> > > think that fixed it.
> > >
> > > Ryan
> >
> > _______________________________________________
> > Xen-users mailing list
> > Xen-users@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-users



-- 
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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