Jonathan Knowles пишет:
However one thing not obvious from the FAQ is that the memory
ballooning daemon is a replaceable component, built separately
from Xapi, and running as a separate service on each XCP host.
George Shuklin replied:
I'm sorry, I think this point is wrong.
Balloon is not a server/dom0 component, it is a kernel module
for domU kernel. It reads from XenStore variables:
static-max = "4194304"
target = "1048576"
dynamic-min = "1048576"
dynamic-max = "1048576"
When I talk about the "memory ballooning daemon", I'm referring
to the following service that runs within domain 0:
/etc/init.d/squeezed
The ballooning daemon is reponsible for choosing, for every VM
running on a host, a target that lies between dynamic-min and
dynamic-max. The ballooning daemon writes targets into XenStore.
The ballooning daemon's default behaviour is to assign targets
proportionally, as described in the previous mail. You can find
more information about it its design here:
http://wiki.xensource.com/xenwiki/squeezed
(courtesy of Dave Scott)
Of course, DMC also relies on each guest having a balloon driver
that responds appropriately to changes in its XenStore target.
So when someone set xe vm-memory-target-set (or dynamic) it
simply order to xapi master to order xapi slaves change those
values and balloon driver in domU will do all work.
The default behaviour of:
xe vm-memory-target-set target=<x>
is equivalent to:
xe vm-memory-dynamic-range-set min=<x> max=<x>
They both directly update the VM.memory-dynamic-{min,max} fields
with the same value.
See the following FAQ section for more details:
http://wiki.xensource.com/xenwiki/Dynamic_Memory_Control
Is there an equivalence between target mode and
dynamic range mode?
George Shuklin replied:
I'd like to announce our own system named MOD (Memory on Demand)
wich one use xenballoon for graceful memory allocating to guest
machines.
Right now it under research and testing, but it looks really
good: it never steal memory to cause oom killer doing it dirty
job.
Main idea: we looking to memory data, calculating free memory
and setting target for xenballoon to preserve some amount of
free memory (We use static-min static-max values as borders
for allowed changes).
I'm intrigued.
Have you considered using dynamic-{min, max} for limits, rather
than static-{min, max}? Using dynamic limits instead of static
limits may give administrators a little more flexibility when
constraining their VMs' memory allocations. (The current design
of XCP allows you to change the dynamic limits while a VM is
running, but changing the static limits requires you to reboot
the VM.)
Right now we using strightforward algorithm 'preserve X MiB of
free memory', in future I think we can switch to some more
intellectual algorithm with prediction system.
Out of interest, how do you measure "free" memory? Do you intend
to count buffer memory as "free"?
I'd be very interested to learn more about your design.
Cheers,
Jonathan
_______________________________________________
xen-api mailing list
xen-api@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/mailman/listinfo/xen-api
| 
Home