Re: [Xen-users] More memory problems.

[J <dreadpiratejeff@xxxxxxxxx>]

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

-- 

Stephen Leacock  - "I detest life-insurance agents: they always argue
that I shall some day die, which is not so." -
http://www.brainyquote.com/quotes/authors/s/stephen_leacock.html

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