On Sat, Mar 06, 2010 at 10:52:37AM +1100, Neil Brown wrote: > But my first suggestion, that splitting could be made easier, still stands. In full agreement we should try to make it easier. > And do you honour merge_bvec_fn's of underlying devices? A quick grep > suggests you do only for dm-linear and dm-crypt. We implemented it to address some specific performance problems reported by people using those targets. So far there hasn't been any pressing need to implement it for other targets. > This suggests to me that it > is actually a hard interface to support completely in a stacked device, so we > might be better off without it. All this code is hard - but very useful. The direction I want to explore when I finally get some time to work on this is one which will probably make more use of, and extend, merge_bvec. > that it makes sense to only require that the lowest level does the > splitting, as that is where the specifics on what might be required exists. We have a hybrid model at the moment - some stuff dealt with top-down, other stuff bottom-up. This thread describes just one of several problems related to this. In the next incarnation of device-mapper I hope we'll find a way to eliminate all of them together. Maybe I'll finally get time later this year to start working on these ideas properly. Alasdair -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
