As I indicated already in this discussion, dm started to use merge_bvec_fn as a cheap way of avoiding splitting and this improved overall efficiency. Often it's better to pay the small price of calling that function to ensure the bio is created the right size in the first place so it won't have to get split later. I'm as yet unconvinced that removing merge_bvec_fn would be an overall win. Some of Kent's other changes that make splitting cheaper will improve the balance in some situations, but that might be handled by simplifying the merge_bvec_fn calculations in those situations. (Or changing the mechanism to avoid repeating performing the mapping when it hasn't changed.) IOW Any proposal to remove merge_bvec_fn from dm needs careful evaluation to ensure it doesn't introduce any significant performance regressions for some sets of users. Alasdair -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
