Dom0 memory allocation?

[tg%gmplib.org@localhost]

Our new machine (Xeon Ivy Bridge X6, 96 GiB ECC RAM, SSD disks) which
runs a bunch of services split over several NetBSD PV DomU, became
messed up last might.

The hardware runs bleading-edge NetBSD 7.0 BETA and Xen 4.5.  Perhaps an
unwise production choice, but there you go.

There are around 20 DomU systems, mostly PVs (running NetBSD and
GNU/Linux) but also a few HVMs (the latter running FreeBSD and OpenBSD
for software testing purposes).

The symptom of last might's problems was that both the guests and the
Dom0 was unresponsive.  I could not run 'top' or 'ps', and /tmp (64 GiB
tmpfs) was "full" but in reality empty.  I managed to unmount /tmp and
therefter got enough control to shut things down gracefully.

Now, I would like to understand what might have happened.

When I tried commands from the shell (like top and ps) I got "Killed"
from the shell.  This smells VM shortage to me.  So perhaps this might
be as simple as inadequate Dom0 RAM allocation allocation?

The system has 96 GiB RAM and 20 DomU's.  I had assigned 1 GiB for Dom0
when this happened, and no swap partition.  I have never seen any
recommendations on how to make an informed choice of Dom0 RAM
allocation.  Could you help?

It seems like Dom0 would need RAM as a function of either guest RAM
allocations or number of guests, or more likely both.

(I have my reasons to not want swap; a thrasing Dom0 seems like a poor
thing.  Instead, I'll give it the RAM it needs.)


-- 
Torbjörn
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