Re: [Xen-devel] How to deallocate memory shared between domain and xen

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 10 Aug 2005, at 02:53, Santos, Jose Renato G wrote:

>   This seems to be working fine.
>   Now, I am not sure what is the sequence of operations to deallocate
> these
>   shared pages when they are not needed anymore. I spent sometime
>   looking at the code but I still don't have a clear understanding
>   of how memory is managed in Xen.
>
>   Any help is greatly appreciated, as will save me a lot of time ...
You want to be able to deallocate them before the domain you were 
sharing with is destroyed? There are no existing examples in Xen of how 
that would be done (things like grant-table pages and shared_info page 
are all destroyed after the domain dies).
Is this the kind of thing you are looking for?:
 1. On allocaction: SHARE_PFN_WITH_DOMAIN(); get_page();
 2. On deallocation: put_page()

...and then the pages get freed up automatically when the guest has 
freed all references. That is: the pages do not get freed until you 
have given up your one reference (put_page) and the guest has given up 
its references.
This can be added quite easily, but will require an new page flag.

 -- Keir


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