Problems with dom0 and low memory

["Jérôme Petazzoni" <jp@enix.org>]

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I am running a Xen box where I need a lot of memory for a given domain 
(which runs memory-hungry java apps). I had reduced the memory of 
domain0 to 42000KB. It *seems* that after running OK for a while, a low 
memory condition on domain0 messed during a short time the VBD of the 
other domains, and they got a burst if I/O errors. After this event, the 
other domains were still running, and their VBD were still working, but 
the burst of I/O errors aborted the ext3 journal on the filesystems 
(causing them to go read-only).

Here are the kernel logs of both domains if you want to check that it's 
indeed a low memory condition problem and not something else (which 
would then be a "real" bug).

I increased the memory allocated to domain0, but it would be interesting 
to know if there is a way to avoid those problems (I thought about 
increasing /proc/sys/vm/min_free_kbytes ; would it be useful here?)

The dom0 and domU kernels, as well as xen itself, the associated 
symbols, and the same log files are located here, if someone needs them:
http://skaya.enix.org/webs/xen/dom0-lowmem/


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