Re: [Xen-API] [XCP] Frequently-Asked Questions (FAQ) for Dynamic Memory Control (DMC)

[George Shuklin <george.shuklin@xxxxxxxxx>]

Thank you very much for document.

But I like to point to one specific problem for current state of memory
management in XCP. By default XCP (in Linux catalogue on xs-tools.iso)
use pv_ops kernel, wich one does not support preinflated balloon. I
belive this is great problem for VM running under XCP: it simply will
not able to grant VM more memory than it have at startup.

The second problem I know is way DMC retrive memory from guests... It
simply ignores memory usage in guest and retrive equal amount of memory
from every running VM. 

Here sample:

Assume we have 5Gb memory for 4 VMs. (And our administrative limits is
dynamic-min 256MiB dynamic-max 2GiB). Every VM will gain about 1.20GiB
memory.

After some time VM 1 lazy waiting anything and use about 100MiB memory.
VM2 is heavy loaded and use about 1.1GiB memory.

Now we starting 5th VM and DMC ballancing memory - it grabs about 200MiB
from every VM to grant new VM it own 1000MiB of memory.

When it grabs 200MiB from lazy machine nothing bad happens... But when
it grabs 200MiB from 1.2GiB machine with 1.1GiB memory usage, or heavy
swapping occur, or, this really ugly: oom killer 'make memory free' in
heavy loaded server.

This is reason I always set dynamic-min==dynamic-max - to DISABLE this
cruel DMC.

Ð ÐÑÐ, 15/09/2010 Ð 12:03 +0100, Jonathan Knowles ÐÐÑÐÑ:
> Hi all
> 
> The v0.5 release of Xen Cloud Platform (XCP) includes support
> for a new feature, known as Dynamic Memory Control (DMC). DMC
> makes it possible to:
> 
>    * change the amount of host physical memory assigned to any
>      running virtual machine, without rebooting it.
>      (within limits specified by an administrator)
> 
>    * start additional virtual machines on a host whose physical
>      memory is currently full, by automatically reducing the
>      memory allocations of existing virtual machines in order
>      to make space.
>      (also within limits specified by an administrator)
> 
> To help share understanding of this feature, we recently added
> a frequently-asked questions (FAQ) page for DMC to the xen.org
> wiki:
> 
> http://wiki.xensource.com/xenwiki/Dynamic_Memory_Control
> 
> Please feel free to write to us on the Xen-API mailing list
> (xen-api@xxxxxxxxxxxxxxxxxxx) with any comments or questions.
> 
> Best wishes
> 
> Jonathan
> 
> -----------------------
> Jonathan Knowles
> Xen Cloud Platform Team
> 
> _______________________________________________
> xen-api mailing list
> xen-api@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/mailman/listinfo/xen-api



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