[Xen-devel] Re: Getting the page fault count for domU

[Chintamani Siddeshwar <chintamani.sid@xxxxxxxxx>]

Okay.
Is it possible to get this info from within Dom0, because Dom0 handles disk paging.
Would it help to look at the backend dd's or the xend?

   thanks
Chintamani

On Mon, Oct 3, 2011 at 8:44 AM, Tim Deegan-6 [via Xen] <[hidden email]> wrote:

At 06:37 -0700 on 03 Oct (1317623870), Chintamani Siddeshwar wrote:

> I am interested in counting the number of page-faults in the guest -
> page-faults that result in a disk I/O.

You will have to do that from inside the guest - only the guest's OS
knows which of its page-faults result in I/O, and on modern (EPT/RVI)
hardware, Xen doesn't even see most guest page-faults.

> Also when would XEN tools page a guest memory to disk? Is it a manual
> process (by running "xenpaging" command) or is it a performance enhancement
> added in recent versions of XEN?

Only when the xenpaging daemon is running.  It is definitely not a
performance enhancement (memory pressure is better dealt with by the
guest) but is useful as a backstop if you're overcommitting memory some
other way.

Tim.

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