On Nov 19, 2007, at 6:40 PM, Sebastian Reitenbach wrote:
Hi,
I try to add a bit memory management monitoring of services within
the Xen
resource, as I am usually interested in the services that the Xen
resource
provides and not whether Xen runs or not. I already got a lot of
valuable
feedback from Dejan, the state can be tracked here:
http://developerbugs.linux-foundation.org/show_bug.cgi?id=1778
The problems right now are:
1) how to handle paused domU's
2) how to handle memory management
The first is a bit work, but easy, before every action check in which
condition the domU is, e.g. running/stopped/paused/... and then
handle that
situation accordingly.
The second one is a bit trickier.
Right now I have the Xen script working this way on startup/stop of
the
domU:
1. check how many memory is available
2. subtract the reserved memory for the dom0
3. check how many domains will after that action running, divide the
result
from step two with that number
4. set xm mem-set the memory for all virtual machines
This is a very basic way to give all virtual machines more or less
the same
amount of memory. Nevertheless, in case more than one Xen resource is
starting or stopping, this behavior is prone to race conditions, and I
already have seen it failing.
My workaround was to create orders, with symmetrical=no and score=0
for all
Xen resources, so that only one can start at a time.
clones have an ordered=true option
it hasn't been used much so it may not be perfect - but if you find
any problems you can be sure i'll fix them promptly
Dejan suggested to add locking to the Xen resource script, but I
fear that
this will lead to new errors, e.g. assume the default-action-
timeout=30s
and you have 4 Xen resources, and all four will start up at the same
time,
then the first, will aquire the lock, the rest is waiting. Maybe
everything
will work for the second Xen resource too. But I assume then the
startup of
3 and 4 will fail, because the default-action-timeout was hit.
Is it possible serialize actions of a given type of resource?
as above, yes :-)
at least for starts and stops
groups, clones and master/slave all support the ordered option and the
lrmd takes care of primitives.
e.g. the Xen resource could be marked as serialization needed, that
means,
in case there are multiple Xen resources in a cluster, actions to
these
resources are not allowed to happen at the same time?
So that not the Xen resource script would be responsible for locking
and
allowing/disallowing actions to itself, but the CRMD is responsible.
This could be made more fine-grained, in case you say, it is not
allowed to
have action for resource Xen at the same time on the same node, but
it is
allowed to have multiple actions to the Xen resource in the cluster.
that we cant do - at the crm level its cluster-wide or not at all
Then the LRMD could be made responsible to serialize the actions.
Does that makes sense to anyone, or maybe is that already possible?
kind regards
Sebastian
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