Something which bothered us at work for some time now is the weird habit of
our Xen servers to report:
Error: (12, 'Cannot allocate memory')
Where we think there is enough (18G free at the moment) to allocate for a
512 Mb virtual machine. I searched high and low for this before but never
found a working answer. With some other changes in the Xen cluster planned
I was looking for answers again to this problem and found:
Xen, HVM, and running out of memory
which shows that the size of dom0 may be causing this. Asking Xen for memory
info gives totally different numbers:
# xm info
..
total_memory : 24570
free_memory : 4
I guess the dom0 has somehow allocated those 18G in a way which Xen can't
get back.
Now to see whether adjusting
dom0_mem will fix this...
Update:
It took longer than expected because other parts of Xen acted up again, but
the Xen cluster is available again with better memory allocation giving us
a lot more space for virtual machine services.
# xm info
..
total_memory : 24570
free_memory : 14668
That is on the machine running most virtual machine services.