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

To: "George Dunlap" <George.Dunlap@xxxxxxxxxxxxx>
Subject: RE: [Xen-devel] what happens when a PoD page is touched?
From: "James Harper" <james.harper@xxxxxxxxxxxxxxxx>
Date: Wed, 18 May 2011 14:52:43 +1000
Cc: Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, Paul Durrant <Paul.Durrant@xxxxxxxxxx>, xen devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Thread-topic: [Xen-devel] what happens when a PoD page is touched?
> The exception to this would be the case where you're allocating N
> pages, where N > (used_pages - total allocation).
> I guess try allocating fewer pages before returning them to Xen, and
> seeing if that helps at all.

I tried returning 64KB at a time (eg 16 pages) instead of 1MB but it
doesn't improve things. Xen should just repopulate every page I allocate
with the pages I just returned and things should fly along but it's not
working that way.

Just taking a step back for a sec, maybe I'm doing something else wrong.
My balloon down code allocates memory from Windows with
MmAllocatePagesForMdlEx then hands the pages to Xen with
XENMEM_decrease_reservation. Is that all I need to do? I notice that
Linux makes a call to set_phys_to_machine(INVALID_P2M_ENTRY) for each
page, even in the hvm case. Is that some function I need to mirror too
or is that just internal Linux housekeeping and not required under



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