Re: [Xen-users] More memory problems.

[James Pifer <jep@xxxxxxxxxxxxxxxx>]

On Tue, 2009-10-06 at 15:21 -0400, J wrote:
> On Tue, Oct 6, 2009 at 15:10, James Pifer <jep@xxxxxxxxxxxxxxxx> wrote:
> > I have several xen servers running on SLES10SP2. I occasionally have
> > problems with allocating memory. When this happens the only fix I know
> > of is to shut down all the domUs and restart the server. Or at least
> > xend, which affects many of my domUs.
> >
> > I have this problem on two servers right now. One of them has plenty of
> > free memory available. See below:
> 
> > When I try to start a domU I get:
> > # xm start lakvre05
> > Error: [Errno 12] Cannot allocate memory
> > Usage: xm start <DomainName>
> >
> > Start a Xend managed domain
> >  -p, --paused                   Do not unpause domain after starting
> > it
> >  -c, --console_autoconnect      Connect to the console after the
> > domain
> >                                 is created
> >
> > Any suggestions for working around this or is restarting xend the only
> > option?
> 
> add dom0_mem=XXXM to the Xen entry (on the first line for this boot
> option) in menu.lst.
> 
> Make XXX something rational for Dom0... I usually set dom0 on my
> systems to 512M or 1024M depending on how much physical ram the system
>  has.
> 
> That usually fixed the problem for me.  The problem is or was (not
> sure if it was ever actually fixed) in the code that handles
> ballooning the memory.  After a while, Xen will just stop shrinking
> Dom0's memory allocation, OR, it's a race and the freeing of memory
> from Dom0 happens slower than the allocating of memory for the new
> DomU.
> 
> Then it gets stuck and the only fix, as you've mentioned, is to reboot.
> 
> So limiting Dom0's memory allocation to something small leaves the
> rest of the system memory unallocated and unused and thus free for
> handing out to DomUs.
> 
> This can also happen if you have a lot of DomUs being installed and
> deleted, or stopped and started frequently.
> 
> Cheers
> Jeff
> 

Unfortunately I already have that set to 2048. Because of previously
issues with this exact problem, I have not had a lot of
starts/stops/reboots/deletes. I don't know what constitutes as "a lot"
though. There are 12 domUs on the server. dom0 has been up for 107 days.
The highest id number for a domU is currently 43. Honestly I'm not sure
how it's even that high.

James


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