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

[Tim Deegan <tim@xxxxxxx>]

Please don't top-post.

At 06:55 -0700 on 03 Oct (1317624948), Chintamani Siddeshwar wrote:
> Okay.
> Is it possible to get this info from within Dom0, because Dom0 handles disk
> paging.

Not unless dom0 can figure out which parts of the guest's disk I/O is
paging and which not.  In some OSes that might be easier than others,
but it will always need knowledge of the guest OS internals and
configuration.

Tim.

> On Mon, Oct 3, 2011 at 8:44 AM, Tim Deegan-6 [via Xen] <
> ml-node+s1045712n4864909h61@xxxxxxxxxxxxx> 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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