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xen-devel
[Xen-devel] Re: Memory fragmentation, order>0 allocation, and 4.0 dynami
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To: |
Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Grzegorz Milos <gm281@xxxxxxxxx>, Patrick Colp <pjcolp@xxxxxxxxx>, Andrew Peace <Andrew.Peace@xxxxxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx> |
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Subject: |
[Xen-devel] Re: Memory fragmentation, order>0 allocation, and 4.0 dynamic RAM optimization features |
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From: |
Keir Fraser <keir.fraser@xxxxxxxxxxxxx> |
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Date: |
Mon, 08 Feb 2010 19:11:24 +0000 |
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Cc: |
Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx> |
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Mon, 08 Feb 2010 11:11:50 -0800 |
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Memory fragmentation, order>0 allocation, and 4.0 dynamic RAM optimization features |
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On 08/02/2010 18:13, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:
> In a recent thread:
>
> http://lists.xensource.com/archives/html/xen-devel/2010-02/msg00295.html
>
> Jan Beulich points out that the memory fragmentation that results
> from Transcendent Memory ("tmem") sometimes causes problems for
> domain creation and PV migration because the shadow code requires
> order=2 allocations and the domain struct is order=4.
>
> Though tmem accelerates fragmentation, I *think* this fragmentation
> can occur with page sharing/swapping, and possibly PoD. In fact,
> I think it can occur even with just ballooning.
>
> I think the domain struct issue should be relatively easy to
> resolve (though maybe with a large patch), but the shadow code
> may be much harder.
I think everything but the shadow use of order-2 allocations is pretty easy
to fix; just a case of logically carving up the multi-page structures.
I'm not sure, but suspect that fragmenting the shadow allocations may
require extra book-keeping space in the page_info structure, for example.
-- Keir
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