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Re: [Xen-devel] RE: [RFC] fix xen_in_range()

To: Jan Beulich <jbeulich@xxxxxxxxxx>, Joseph Cihula <joseph.cihula@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] RE: [RFC] fix xen_in_range()
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Fri, 24 Apr 2009 08:16:12 +0100
Cc: Dexuan Cui <dexuan.cui@xxxxxxxxx>, Shane Wang <shane.wang@xxxxxxxxx>, Yunhong Jiang <yunhong.jiang@xxxxxxxxx>, Xiaowei Yang <xiaowei.yang@xxxxxxxxx>, Liping Ke <liping.ke@xxxxxxxxx>, Xin Li <xin.li@xxxxxxxxx>
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On 24/04/2009 08:04, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

> Also, after suggesting to use gb-pages when possible here I realized that
> it's probably a latent bug to map more space than was allocated - if the
> non-allocated-but-mapped pages happen to later get allocated to a domain,
> that domain may change the cacheability attributes of any of these pages,
> resulting in aliasing issues. I'll put together a patch for this, but it'll be
> a couple of days until I'll be able to do so.

I think we should shatter the superpage on demand. This would also be
required for superpage mappings of Xen itself: when we free initmem that
memory can now be allocated to a domain (now xenheap and domheap are merged
on x86/64).

An alternative might be to mark such partially-freed superpages as
Xenheap-only, and allocate them preferentially for Xenheap callers (i.e.,
alloc those pages first, then from the general heap).

 -- Keir

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