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Re: [Xen-devel] [PATCH 1/2] PV hugepages - Xen patch

To: Dave McCracken <dcm@xxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 1/2] PV hugepages - Xen patch
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Wed, 08 Oct 2008 19:50:16 +0100
Cc: Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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On 8/10/08 19:28, "Dave McCracken" <dcm@xxxxxxxx> wrote:

>> Actually this is an interesting one. For a PV guest it may be in general
>> unsolvable, since the target machine may not have allocatable 2MB extents.
>> It may also screw live migration since 2MB is a very coarse granularity to
>> do dirty-page tracking. One option: perhaps the PV kernel could shatter and
>> then reconstruct (as best it can) superpage mappings across save/restore?
>> I'm actually not sure what's for the best here. Perhaps just make 2MB
>> mappings and save/restore mutually exclusive for now?
> 
> Yeah, that's what I'm finding.  I think it's a good idea to document for now
> that hugepages don't work with save/restore.  I'll continue to dig into it
> and try to figure out a scheme to make it work as a future enhancement.

Then PV superpage support must be a configuration option, and disabled by
default.

 -- Keir



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