[CentOS-virt] Xen DomU's randomly freezing

Mon Apr 30 12:08:26 UTC 2018
Daz Day <dazday60 at gmail.com>


I've tried hitting up the CentOS forums and thought I'd try here too as I
don't seem to be getting any bites.

We've been in the process of migrating all our hypervisors over to CentOS 7
using Xen. Once we had a few up and running we started to notice that the
DomU's would randomly freeze. They become unresponsive to any network
traffic, stop consuming CPU resources on the hypervisor and it's not
possible to log in to the console locally using:
virsh console <domain>
We can sometimes get as far as typing a username and hitting return, but
the DomU just hangs there. It doesn't seem to matter what Linux distro the
DomU is running, it affects them all. The only way we can get them back is
by destroying and recreating them (far from ideal!).

After a bit of research and digging around, we eventually found these 2

They both advise adding the command line argument:
gnttab_max_frames=256(the default is 32).
We applied this change and all hypervisors rand stable for around a week
until DomU's started freezing again (we've since tried even higher values,
to no avail). More research later led me to
https://bugs.centos.org/view.php?id=14258 and
https://bugs.centos.org/view.php?id=14284 (which are essentially the same
report). There hasn't really been any movement on these tickets
unfortunately, but I have +1'd them.

Have any others had issues with Xen and DomU's locking up in CentOS 7? Are
there any other fixes/workarounds? If any additional info is needed that
isn't already in the bug tickets or forum post, please let me know and I'll
be happy to provide whatever is required (these freezes are happening at
least once a day).

Any help would be much appreciated and would mean my Ops guys could get a
decent sleep!
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