Xen devel - Oct 2007 - Limit on the number of grant-table mapped pages

Hi list,

I am using xen-3.1 and am particularly interested in the recently added
user-space grant table device. I am trying to build a small communication
channel for passing data among user level processes.

I find that the maximum number pages that can be mapped through the grant
table device is currently hard coded to 128. And I was under the
impression that earlier Xen supports 1k pages (per domain) to be mapped to
other domains in maximum.

Thus, I am asking if it is possible to increase this limit? And if so,
what is the current upper limit that we can mapped from each domain? Or is
it simply a macro define somewhere in the Xen kernel?

Thanks a lot!

-- Wei



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Hi Wei,

The 128 page limit in gntdev was chosen to provide a useful number of  
mappings without occupying too much kernel memory, and you can safely  
increase its value. Future work for gntdev includes making this size  
configurable at runtime and/or making it resizable.

The limiting factor seems to be the maximum number of maptrack  
entries, which appears to be configurable by redefining the  
MAX_MAPTRACK_TO_GRANTS_RATIO, and setting the gnttab_max_nr_frames  
parameter.

Regards,

Derek Murray.

On 17 Oct 2007, at 19:24, wei huang wrote:
> Hi list,
>
> I am using xen-3.1 and am particularly interested in the recently  
> added
> user-space grant table device. I am trying to build a small  
> communication
> channel for passing data among user level processes.
>
> I find that the maximum number pages that can be mapped through the  
> grant
> table device is currently hard coded to 128. And I was under the
> impression that earlier Xen supports 1k pages (per domain) to be  
> mapped to
> other domains in maximum.
>
> Thus, I am asking if it is possible to increase this limit? And if so,
> what is the current upper limit that we can mapped from each  
> domain? Or is
> it simply a macro define somewhere in the Xen kernel?
>
> Thanks a lot!
>
> -- Wei
>
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel

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