Re: [Xen-users] Can't Allocate Memory

["Jeff Lane" <sundowner225@xxxxxxxxx>]

On Tue, Jul 8, 2008 at 11:49 AM, James Pifer <jep@xxxxxxxxxxxxxxxx> wrote:
> I've had this problem on several occasions and it's a pain. When I try
> configure another domU using virt-manager I get a can't allocate memory
> error. My dom0 is limited with the startup parameter dom0_mem=2048M. The
> system has 14 gig of RAM. It's running SLES 10SP1. It let's me select
> the amount of RAM and says 8GB is available. In this case I'm only
> choosing 512meg.
>
> I know if I restart the server, or stop and restart xend and xendomains
> it will clear up this issue, for a while anyway.
>
> Is there any way to clear things up without a restart? I really don't
> want to bring down the other running domU's.

None that I know of.  I've run into this issue many times in test,
with both RHEL and SLES and it's an ongoing problem that no one seems
to be able to resolve.  The other issue is that this is not
necessarily easy to reproduce either.

The oddity here is that you are still seeing the problem.  In every
case I've run across, limiting dom0 like you've done resolved the
problem.

This makes me wonder a few things...

1:  how many domUs do you have running, and what are their memory limits?
2:  Have you tried a full restart, along with limiting the max memory
for each domU to ensure that the guests don't try grabbing too much
memory? As I recall, besides limiting dom0's max, if you don't limit
the domU max they too will be able to grab additional RAM.
3:  Are you in a scenario where you are starting and stopping them
repeatedly?  That's more a curiosity for me, as I wonder if you are
stopping some guests and their memory is not being released to the
pool for other guests to grab as they are started.
4:  Not that it makes THAT much difference, but are you running 32bit
or 64bit SLES?
5:  Finally, again, not that it should make too much difference, but
if this is a NUMA capable machine, are you enabling NUMA at boot time?
 I don't know that NUMA would do anything to help or hinder here, but
it's a thought at least.

I am not a Xen developer or anything, but I'm curious about this as
well.  As I said, I've seen this myself on both RHEL and SLES, going
back to RHEL 5.0 and SLES 10 all the way through RHEL 5.2 and SLES 10
SP2 in testing.

Good luck...

Jeff

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