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[Xen-devel] Re: revisit the super page support in HVM restore

To: "Zhai, Edwin" <edwin.zhai@xxxxxxxxx>
Subject: [Xen-devel] Re: revisit the super page support in HVM restore
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Wed, 19 Aug 2009 08:29:18 +0100
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On 19/08/2009 08:08, "Zhai, Edwin" <edwin.zhai@xxxxxxxxx> wrote:

> So how about this new method:
> * Not tracking each of pfn inside 2M page, but trying best to allocate
>   2M pages if the 2M page covering this pfn is not allocated.
> * There may be holes inside new allocated 2M pages that are not synced in
>   this batch, but we don't care and assume these missing pfns will
>   come in future.
> This new method is simple as the super page support for PV guest is
> already there.

You wil fail to restore a guest which has ballooned down its memory as there
will be 4k holes in its memory map. You will allocate 2MB superpages despite
these holes, which do not get fixed up until end of restore process, and run
out of memory in the host, or against the guest's maxmem limit.

 -- Keir

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