On Mon, Aug 15, 2011 at 11:47:53AM -0400, Jeff Moyer wrote: ... > Now, however, we don't get into the flush machinery at all. Instead, > __elv_next_request just hands a request with flush and fua bits set to > the scsi_request_fn, even if the underlying request_queue does not > support flush or fua. > > The agreed upon approach is to fix the flush machinery to allow > stacking. While this isn't used in practice (since there is only one > request-based dm target, and that target will now reflect the flush > flags of the underlying device), it does future-proof the solution, and > make it function as designed. > > In order to make this work, I had to add a field to the struct request, > inside the flush structure (to store the original req->end_io). Shaohua > had suggested overloading the union with rb_node and completion_data, > but the completion data is used by device mapper and can also be used by > other drivers. So, I didn't see a way around the additional field. > > I tested this patch on an HP EVA with both ext4 and xfs, and it recovers > the lost performance. Comments and other testers, as always, are > appreciated. > > Cheers, > Jeff > > Signed-off-by: Jeff Moyer <jmoyer@xxxxxxxxxx> Acked-by: Tejun Heo <tj@xxxxxxxxxx> Thanks a lot for the persistence. :) -- tejun -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
