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Re: [Xen-devel] Limit on the number of grant-table mapped pages



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



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