Re: [Xen-devel] Linux grant map/unmap improvement proposal (Draft B)

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Mon, 2014-10-13 at 14:41 +0100, David Vrabel wrote:
> Safe grant unmap
> ----------------
> 
> Grant references will only be unmapped when they are no longer in use.
> i.e., the page reference count is one.
> 
>     int gnttab_unmap_refs_async(struct gnttab_unmap_grant_ref *unmap_ops,
>         struct gnttab_unmap_grant_ref *kunmap_ops,
>         struct page **pages, unsigned int count,
>         void (*done)(void *data), void *data);
> 
> The `gnttab_unmap_refs_async()` function will unmap the grant
> references using the supplied unmap operations and call `done(data)`.
> The grant unmap will only be done once all pages are no longer in use.
> 
> It shall run synchronously on the first attempt (this is expected to
> be the most common case).  If any page is in use, it shall queue the
> unmap request to be tried at a later time.
> 
> Only the blkback and gntdev devices need to use asynchronouse unmaps.

What about storage over networking? Does this work for that case too? I
suppose that would just manifest as >1 reference counts when the blk op
finishes, which would be taken care of by the delay.

Ian.


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