Re: [Xen-devel] [PATCH 3/4] xen: arm: rearrange guest physical address space to increase max RAM

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2014-04-08 at 17:01 +0100, Julien Grall wrote:

> >> Also, can you make sure that the GNTTAB_SIZE is greater or equal to the
> >> maximum number of frames (maybe by overriding max_nr_grant_frames)?
> > 
> > It turns out that the current size corresponds to
> > DEFAULT_MAX_NR_GRANT_FRAMES, which explains where it came from.
> 
> I know it... a comment in the code here would be great to avoid loosing
> 20mins every time we hit this define.

Feel free to send a patch.

> > If you want to change this to reserve say 1MB of address space (which is
> > enough for 256 grant pages) or even more then please send a patch.
> > 
> >> The current implementation on Linux only care about the number of frames
> >> given by Xen, the size of the table in the DT is not used. So the range
> >> may overlap to something else.
> > 
> > That would be a guest bug, but nothing to do with this series.
> 
> It's not really a guest bug ... we have an hypercall which provides the
> GNTTAB size (see gnttab_query_size).
> 
> It returns max_nr_grant_frames which can be modified by the Xen command
> line.

The tools could query this and use it to size the region, or we could
just make the region be more than large enough. Patches welcome.

Ian.


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