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Re: [Xen-devel] Re: super page with live migration

To: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Subject: Re: [Xen-devel] Re: super page with live migration
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Fri, 26 Sep 2008 10:28:12 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, "Zhai, Edwin" <edwin.zhai@xxxxxxxxx>
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On 26/9/08 10:08, "Tim Deegan" <Tim.Deegan@xxxxxxxxxx> wrote:

> At 10:03 +0100 on 26 Sep (1222423431), Keir Fraser wrote:
>> Yes: If pseudo-phys page is not yet populated in target domain, AND it is
>> first page of a 2MB extent, AND no other pages in that extent are yet
>> populated, AND the next pages in the save-image stream populate that extent
>> in order, THEN allocate a superpage. This is made trickier by the fact that
>> the next 511 pages (to make the 2MB extent) might be split across a batch
>> boundary. So we'll have to optimistically allocate a superpage in that case,
>> and then shatter it if it turns out that the contiguous stream of
>> pseudo-phys addresses is broken in the next batch.
> Or flag the start-of-a-superpage frames when saving them?

It's not clear to me this is significantly easier to hack in on the save
side, and restore side would still need modifying, and it would change the
save format (albeit probably not hard to do it in a backward-compatible
way). I'm not absolutely dead set on my stated approach though.

 -- Keir

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