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Re: [Xen-devel] Different: nr_pages vs. max_pfn

  • To: "Y. D." <duyuyang@xxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
  • Date: Wed, 19 Nov 2008 09:54:27 +0000
  • Cc:
  • Delivery-date: Wed, 19 Nov 2008 01:54:50 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AclKLM8UDVgd9LYgEd2n/QAWy6hiGQ==
  • Thread-topic: [Xen-devel] Different: nr_pages vs. max_pfn

The shared_info value is set up by the guest itself during boot. It's larger
because Linux adds extra space at the end of its p2m map for backend

 -- Keir

On 19/11/08 09:45, "Y. D." <duyuyang@xxxxxxxxx> wrote:

> Hi,
> In start_info, there is a field nr_pages definig how much memory is allocated
> to the domain, which is obvious.
> While in shared_info, there is a field max_pfn. I don't know why max_pfn is
> not equal to nr_pages.
> Say for 32MB memory, nr_pages = 8192, while max_pfn = 10240 (may vary?), of
> which 2048 pfn's have invalid mfn.
> Can anybody explain that why max_pfn is larger? Is it static or dynamic?
> Furture, does pfn to mfn frame mapping ever change? Hopefully not.
> Thanks,
> Shawn
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