On Jul 13, 2015, at 2:47 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > On Sun, Jul 12, 2015 at 02:15:56PM -0400, Chuck Lever wrote: >>> Chuck, Would a scatterlist API make life easier for you? >> >> No benefit for me. >> >> The NFS upper layer already slices and dices I/O until it is a >> stream of contiguous single I/O requests for the server. >> >> It passes down a vector of struct page pointers which xprtrdma?s >> memory registration logic has to walk through and convert into >> something the provider can deal with. >> >> See fmr_op_map and frwr_op_map. The loop in there becomes costly >> as the number of pages involved in an I/O request increases. >> >> I suppose an s/g list wouldn?t be much different from the current >> arrangement. And if NFS and SunRPC are the only users that deal >> with struct page, then there?s no code sharing benefit to >> providing a provider API based on struct page. > > NFS really should be using something more similar to a scatterlist, > as it maps pretty well to the sk_frags in the network layer as well. > > Struct scatterlist is imprtant because it's the way the DMA mapping > functions takes a multi-page argument, so ayone who wants to batch > the S/G mapping calls needs it. An excellent topic to bring up on linux-nfs@xxxxxxxxxxxxxxx. In the meantime, I think rpcrdma.ko would have to be responsible for converting struct page to struct scatterlist. -- Chuck Lever -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
