On Thu, Mar 29, 2018 at 11:02:10AM -0600, Logan Gunthorpe wrote: > Per the bug in the previous patch, I don't think that was ever a valid > assumption. It doesn't have anything to do with the sgl_alloc change > either. The dma_map interface is allowed to merge SGLs and that's why it > can return fewer nents than it was passed. I'm not sure how many or > which DMA ops actually do this which is why it hasn't actually > manifested itself as a bug; but it is part of how the interface is > specified to work.
Most iommus can, it just is very unlikely do happen in block drivers given that the block layer already merges segments higher up.
