On Mon, Mar 03, 2008 at 02:10:17PM +0100, Nick Piggin wrote: > Is this just a GRU problem? Can't we just require them to take a ref > on the page (IIRC Jack said GRU could be changed to more like a TLB > model).
Yes, it's just a GRU problem, it tries to optimize performance by calling follow_page only in the fast path, and fallbacks to get_user_pages; put_page in the slow path. xpmem could also send the message in _begin and wait the message in _end, to reduce the wait time. But if you forge GRU to call get_user_pages only (like KVM does), the _begin can be removed. In theory we could also optimize KVM to use follow_page only if the pte is already established. I'm not sure how much that is a worthwhile optimization though. However note that Quadrics also had a callback before and one after, so they may be using the callback before for similar optimizations. But functionality-wise _end is the only required bit if everyone takes refcounts like KVM and XPMEM do. ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
