Xen devel - Jun 2006 - detecting paging inside of VMs

I''d like to be able to detect when a VM is pressed for memory without
doing
anything inside of the VM.

My idea is to add some code in the hypervisor that would try to detect
paging in each domU, or maybe just monitor the rate at which memory pages
are being requested and released.

I know that the guest OSes are responsible for managing their own page
tables, but I suspect that some of this still goes through the VMM.

I''m willing to do some hacking, but I''m not yet sure if the
information I''d
need can be obtained in the hypervisor.  I''d rather not modify the user
level xen kernels if possible.

Does any of this seem plausible?  Thanks for any info!

-Tim

p.s. of course if you have any other ideas (that are transparent to the
domU) I''d be interested to hear


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On 21 Jun 2006, at 16:10, Tim Wood wrote:
> I''d like to be able to detect when a VM is pressed for memory
without
> doing anything inside of the VM. 
>
> My idea is to add some code in the hypervisor that would try to detect 
> paging in each domU, or maybe just monitor the rate at which memory 
> pages are being requested and released.
>
> I know that the guest OSes are responsible for managing their own page 
> tables, but I suspect that some of this still goes through the VMM.
If you know the domU has a swap partition then you could modify blkback 
driver in dom0 (or pull stats out of it somehow) to detect swap 
activity. Dom0 seems a better probe point than Xen -- it knows about 
I/O and it will also be the place where you implement policy to decide 
who gets what memory.

  -- Keir


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