Xen devel - Aug 2004 - simple question on frontend network driver and decreasing reservation

the frontend driver, in network_alloc_rx_buffers, allocates pages and then 
hands them off to xen for the rx ring, using MEMOP_decrease_reservation. 
Just checking, but I assume this actually decreases the domain''s 
allowed memory footprint? 

At poll_if time, it reclaims pages from the rx queue by mapping them back 
in (I hope I got this right). 

Now I assume that as it pulls those pages back in to the domain, the 
domain''s allowed page count is increased for each page it pulls in?
Just
curious. 

thanks

ron



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That all sounds right.
Giving up the pages from the guest decreases the number of pages the domain 
actually owns, you should see the page count for that domain varies.

The backend assigns pages back to the domain as and when data arrives to fill 
them and notifies the domain via the shared memory interface.  The domain is 
then able to map them into its address space.

The page count of the guest will go up immediately the backend reassigns their 
ownership, regardless of whether the guest remaps them.  When the guest maps 
them, their ref count gets incremented.

By the way, on an unrelated note, how are you planning on tackling the GUI in 
Plan 9?  Or are you mainly aiming at backend servers?  I''d like to be
able to
run Plan 9 but I''m not sure I can dedicate a machine to it (mainly
because I
doubt it would like my hardware).

Cheers,
Mark



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On Wed, 1 Sep 2004, Mark Williamson wrote:
> By the way, on an unrelated note, how are you planning on tackling the GUI
in
> Plan 9?  Or are you mainly aiming at backend servers?  
First cut is just an auth server and fossil server and CPU servers. I just 
want them to work at all. For a cpu server, you can drawterm to it from 
Linux and get the full Plan 9 GUI (more or less) while not needing to have 
Plan 9 own graphics hardware. It''s the next best thing to being there
:-)

I''m hoping to get the frontend block driver next, then dedicate some
real
disk partitons to Plan 9 guests, but we''ll see. 

I am hoping against hope that we can find a way in 2.0 to hand over
virtual consoles from DOM0 to Plan 9, but have no idea if that is even
possible. So the graphics thing comes later. But it would be nice to solve 
it. 
>I''d like to be able to 
> run Plan 9 but I''m not sure I can dedicate a machine to it (mainly
> because I doubt it would like my hardware).
That''s the big goal. I started this project because of the number of 
people who can''t run plan 9 on their hardware. It''s a spare
time thing but
it has helped me learn a lot about Xen, so it''s worth it. 

thanks

ron



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