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[Xen-devel] Re: Memory fragmentation, order>0 allocation, and 4.0 dynami

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>
Subject: [Xen-devel] Re: Memory fragmentation, order>0 allocation, and 4.0 dynamic RAM optimization features
From: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Date: Tue, 9 Feb 2010 10:50:10 +0000
Cc: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, Patrick Colp <pjcolp@xxxxxxxxx>, Milos <gm281@xxxxxxxxx>, Grzegorz, Andrew Peace <Andrew.Peace@xxxxxxxxxxxxx>
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At 19:11 +0000 on 08 Feb (1265656284), Keir Fraser wrote:
> 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.

I think it can be done without expanding page_info, but it involves
pretty invasive changes to all the parts of the shadow code that deal
with guest<->shadow mappings and with iterating across shadows.

As I said in response to an earlier email, I think the right thing to do
here is to move pretty much all allocation in Xen to superpage
granularity (and not just because it makes this issue go away!).

Tim

-- 
Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, XenServer Engineering
Citrix Systems UK Ltd.  (Company #02937203, SL9 0BG)

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