Different: nr_pages vs. max_pfn

Different: nr_pages vs. max_pfn

[Y. D.]

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

Re: Different: nr_pages vs. max_pfn

[Keir Fraser]

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
drivers.

 -- Keir

On 19/11/08 09:45, "Y. D." <duyuyang@gmail.com> 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
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel

RE: Different: nr_pages vs. max_pfn

[Jayaraman, Bhaskar]

Keir, does Dom0 Linux do this for each Mini-OS instance that is spawned? If so then shouldn't the memory usage value in xm list for each PV guest take into account this additional usage of memory? i.e. 32MB + 8MB?

Bhaskar.

-----Original Message-----
From: xen-devel-bounces@lists.xensource.com [mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of Keir Fraser
Sent: Wednesday, November 19, 2008 3:24 PM
To: Y. D.; xen-devel
Subject: Re: [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
drivers.

 -- Keir

On 19/11/08 09:45, "Y. D." <duyuyang@gmail.com> 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
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel



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Re: RE: Different: nr_pages vs. max_pfn

[Y. D.]

>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
>drivers.

I tested for various memories, i.e. 64M and 128M, the extra memory is 8M unchanged.
Also, I tested the extra 8M memory is dispersed in the p2m map, not at the end totally.
Can we say the p2m mapping table stays put during dom's lifecycle?

Thanks, keir.

Shawn