Hello Avi,

On Sun, 2010-08-01 at 11:18 +0300, Avi Kivity wrote:
> I don't understand.  Under what conditions do you use
> get_user_pages() 
> instead of get_user_pages_fast()?  Why?

The code always calls get_user_pages_fast, however, the page will be
unpinned in skb_free if the same page is not used again for a new
buffer. The reason for unpin the page is we don't want to pin all of the
guest kernel memory(memory over commit). So get_user_pages_fast will
call slow path get_user_pages. 

Your previous comment is suggesting to keep the page pinned for
get_user_pages_fast fast path?

Thanks
Shirley