Hi Damien! > Modify blk_apply_bdi_limits() to use a device max_sectors limit to > calculate the ra_pages field of struct backing_dev_info, when the > device is a rotational one (BLK_FEAT_ROTATIONAL feature is set). I much prefer doing it here. I don't think overriding io_opt in SCSI is appropriate. Applications and filesystems need to be able to determine whether a SCSI device reports an optimal I/O size or not. Overloading the queue limit with readahead semantics does not belong in SCSI. > For a SCSI disk, this defaults to 2560 KB, which significantly improve > performance for buffered reads. I believe this number came from a common RAID stripe configuration at the time. However, it's really not a great default and has caused problems with many devices that expect a power of two. Personally, I'd like this default to be something like 2MB or 4MB. MD, DM, and most hardware RAID devices report their stripe width correctly so the existing "RAID-friendly" default really shouldn't be needed. Anyway. That's orthogonal to this particular change... Reviewed-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx> -- Martin K. Petersen
