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RE: [Xen-users] OOM killer observed during heavy I/O from VMs (XEN3.0.4 and XEN 3.1)



            I got this error also by 384 MB (having 7 linux VMs and 1 W2K HVM on Xen 3.1.0 under Debian Etch Dom0), the oom-killer till now always selected the W2K instance to kill...


            I think this is very dependent on the fact if the DOmU is on LVM and especially if there is some snapshot of it – then If You for example copy by „dd“ the new image on such a partition, which has a snapshot, the LVM subsystem has to allocate a lot of memory on the disk for the new blocks in snapshot and it looks to lead to the given memory problem. If I dropped the snapshot partition and used smaller blocksize in dd, it has been no problem.


            Sure, to have the snapshot of the partition which is going completely to be changed is not goor, I just have forgotten to drop the snapshot I created for backup purposes before...


            I have read somwhere, there can be prevented some process from beeing killed by the oom-killer, but I do not know how to apply it to the given domain after it has been started...


            In http://linux-mm.org/OOM_Killer there is written „Any particular process leader may be immunized against the oom killer if the value of it's /proc/<pid>/oomadj is set to the constant OOM_DISABLE (currently defined as -17).“, but how can I figure out which process is the process serving my DomU? And what can happen with the LVM subsystem if the memory is not increased because no DomU can be killed by oom-killer?


            Does anybody have experiences with it?


                        With regards,





From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Eric Tessler
Sent: Friday, August 10, 2007 6:26 AM
To: Thomas Mueller; xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] OOM killer observed during heavy I/O from VMs (XEN3.0.4 and XEN 3.1)


Can you send me your OOM killer output from /var/log/messages - I want to see if it's the same one that I am hitting.


If we increase our memory to 384MB of higher, we don't get the OOM killer - at least we have not seen it yet (we want to keep dom0 to 256MB).



Thomas Mueller <tmu@xxxxxxxxxxxx> wrote:

hi there

> Under both XEN 3.0.4 ( and XEN 3.1 (2.6.18), I can make the
OOM killer
> appear in dom0 of my server by doing heavy I/O from within a
> VM.

just wanted to say, that i'm facing probably the same problem with XEN
3.1 and 256MB RAM in dom0. I also had this with 512MB but not so often.
Sometimes this happens if i "dd" a new file-image (10GB) in dom0.

- Thomas

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