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Re: [Xen-devel] Re: non-contiguous allocations

To: Jan Beulich <JBeulich@xxxxxxxxxx>, Olaf Hering <olaf@xxxxxxxxx>
Subject: Re: [Xen-devel] Re: non-contiguous allocations
From: Keir Fraser <keir@xxxxxxx>
Date: Mon, 09 May 2011 09:34:37 +0100
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Thread-topic: [Xen-devel] Re: non-contiguous allocations
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On 09/05/2011 09:30, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:

>> Yes, sticking with alloc_xenheap_pages() is good.
> It really depends on whether you expect to get memory that has
> (even on 32-bit) a virtual mapping, or you want to map it at an
> arbitrary virtual address after wards. alloc_xenheap_pages() gives
> you mapped memory (and the amount you can get is rather limited
> on 32-bit), while alloc_domheap_pages(NULL, ...) gives you
> memory that has a mapping only on 64-bit (and, once we'll find it
> necessary to support machines with more than 5Tb, even that
> may not hold anymore) but it equally not associated with any
> domain.

We have a mechanism for sharing xenheap pages with a guest, which xentrace
is already using. Doing the same with anonymous domheap pages would be extra
hassle. The limitation of xenheap on x86_32 is uninteresting to me,
especially when we're talking about a niche developer feature like xentrace.

 -- Keir

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