On Fri, May 22, 2020 at 09:36:18AM -0400, Martin K. Petersen wrote: > > >>> + if (t->io_opt & (t->physical_block_size - 1)) > >>> + t->io_opt = lcm(t->io_opt, t->physical_block_size); > > > >> Any comment on this patch ? Note: the patch the patch "nvme: Fix > >> io_opt limit setting" is already queued for 5.8. > > > > Setting io_opt to the physical block size is not correct. > > Oh, missed the lcm(). But I'm still concerned about twiddling io_opt to > a value different than the one reported by an underlying device. > > Setting io_opt to something that's less than a full stripe width in a > RAID, for instance, doesn't produce the expected result. So I think I'd > prefer not to set io_opt at all if it isn't consistent across all the > stacked devices. We already modify the stacked io_opt value if the two request_queues report different io_opt's. If, however, only one reports an io_opt value, and it happens to not align with the other's physical block size, the code currently rejects stacking those devices. Damien's patch should just set a larger io_opt value that aligns with both, so if one io_opt is a RAID stripe size, the stacked result will be multiple stripes. I think that makes sense, but please do let us know if you think such mismatched devices just shouldn't stack. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
