[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Problem with PV disk and iSCSI
On 11/2/08 15:26, "Gary Grebus" <ggrebus@xxxxxxxxxxxxxxx> wrote: >> netback already does this kind of reference counting. It oughtn't to be hard >> to check the page reference count in the blkback I/O completion handler and, >> if non-zero, set up a callback for when the count does fall to zero. And >> defer responding to the frontend until that time. Netback is even more >> sophisticated in that it also sets a time out and if the page languishes for >> too long with non-zero count, it's able to forcibly copy-and-release the >> page. I don't think we need to go that far for blkback however. > > In the failure I'm seeing, the skb could sit on a socket queue > indefinitely. The application reading the socket could be blocked for > some other reason. blkback can't defer responding to blkfront > (completing the guest I/O). > > I think blkback needs to assume that a completion with a non-zero page > reference count means it needs to make a copy, or implement a timeout > like netback. Either way, most of the infrastructure you need should be there, and you can crib from netback to work out how to use it. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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