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RE: [Xen-devel] what happens when a PoD page is touched?

To: "Paul Durrant" <Paul.Durrant@xxxxxxxxxx>, "Tim Deegan" <Tim.Deegan@xxxxxxxxxxxxx>
Subject: RE: [Xen-devel] what happens when a PoD page is touched?
From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
Date: Tue, 17 May 2011 09:39:34 +1000
Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, xen devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Thread-topic: [Xen-devel] what happens when a PoD page is touched?
> > -----Original Message-----
> >
> > I've not seen any slowdown on boot with any version of Windows until
> > I go to actually do the balloon down...
> >
> In that case I guess your slowdown is caused by touching the pages.
IIRC you
> will encounter a sweep every time you touch a pod page and the cache
> exhausted. The sweep should reap all zeroed pages and hopefully fill
the cache
> so the sweep should not be invoked too often. Try using the
> allocator.

So avoiding the sweep is the thing to do then?

Where does the sweep start? Does it sweep in physical address order from
lowest address to highest? If I allocated some memory with a low
physical address and zero'd it and then didn't touch it would that be
found first?

Alternatively, I balloon down 1MB of memory at a time - if I could set
aside 1MB of memory that was filled with 0's and could somehow tell xen
to use that memory first then it might speed things up too yes?



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