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

["Jeff Lane" <sundowner225@xxxxxxxxx>]

On Tue, Jul 8, 2008 at 12:52 PM, James Pifer <jep@xxxxxxxxxxxxxxxx> wrote:
> Total system RAM 14gb.
> dom0 = 2gb
> server1 (full) = 3gb
> server2 (full) = 1gb
> server3 (para) = 3gb (NOT running)
> server4 (para) = 1gb
> server5 (full) = 512meg ï (NOT running)
> server6 (full) = 512meg
> server7 (full) = 1gb ï (NOT running)
> server8 (full) = 512mg ï (NOT running)

So overall, 12.5GB worth of Domains, dom0 inclusive, and 14GB total
system ram...  doesn't Xen also have some overhead in the neighborhood
of 1 - 2 GB for the Hypervisor as well?

By "NOT running" do you mean that they WERE running but are stopped
now, or that none of those will start at all?

I'm leaning toward the "memory not being released" hypothesis here...
I've never seen Igor's suggestion before, but xm delete SHOULD free
any resources reserved by the domUs being deleted.  In any case, Why
not? :-)

> Was not aware you could/should limit the domU's. Can you tell me that
> setting? I'm willing to try it, but according to virt-manager they are
> all using what they are supposed to.

I've never had to before, but you can limit the domU's max ram
allowance via a line in the domUs config file in /etc/xen or via xm.
I'm not positive what the actual parameter is of the top of my head
though, but it should be listed in docs somewhere... and if you do an
xm --help or something along those lines, you should get a full list
of xm parameters to let you limit them on the fly.

supposedly, man 5 xmdomain.cfg should give you the domain config
format.  Also, this may help too:

http://wiki.rpath.com/wiki/Xen_DomU_Guide

I don't know that limiting max mem for a guest is absolutely
necessary, but since you are really getting the most out of your
available RAM, it certainly wouldn't hurt to put some limits in place.
 At least, that "should" guarantee that guests are not grabbing any
more than necessary.

> Not really, but their certainly has been a number of stops and
> restarts.

Yep... now I am really betting on ram not being freed up after domains
are shut down.  Again... bug, IMO.

>> 4:  Not that it makes THAT much difference, but are you running 32bit
>> or 64bit SLES?
>
> 64bit

Ok... like I said, not that it matters, really, but at least that
rules out any 32Bit memory handling weirdness.

> Don't know if it's NUMA capable. This machine is an HP DL360-G5. I don't
> see any NUMA parameter in the boot parameters.

I have no idea.  Google didn't even turn up anything useful.  You
could always try passing numa=on to the kernel line in grub... I am
pretty sure that on a non-NUMA system, that won't do anything.  But on
a NUMA system, it will at least enable it.  SLES and RHEL do not
enable NUMA by default in Xen, so you have to explicitly turn it on.
BUT, to be honest, I couldn't even find it mentioned on the HP website
for the DL-360 G5, and I'd imagine that that is something they would
certainly include in their marketing schwag as a feature...

Of course, I saw some post somewhere about having a "Memory Affinity"
option in BIOS setup if the system is NUMA aware...  I have all IBM
boxen, and I am pretty sure they do not have a Memory Affinity option
in BIOS, so YMMV.

But certainly try Igor's suggestion.  And let me know if that works
for you, as that could help my and my people out as well.

Cheers
Jeff



-- 
------------------> Jeffrey Lane - W4KDH <-------------------
 www.jefflane.org
 Another cog in the great
 Corporate Wheel

The internet has no government, no constitution, no laws, no
rights, no police, no courts. Don't talk about fairness or
innocence, and don't talk about what should be done. Instead,
talk about what is being done and what will be done by the
amorphous unreachable undefinable blob called "the internet
user base." -Paul Vixie

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