On Wed, Sep 02 2020 at 11:11am -0400, Christoph Hellwig <hch@xxxxxx> wrote: > On Wed, Aug 26, 2020 at 06:07:38PM -0400, Mike Snitzer wrote: > > On Sun, Jul 26 2020 at 11:03am -0400, > > Christoph Hellwig <hch@xxxxxx> wrote: > > > > > Drivers shouldn't really mess with the readahead size, as that is a VM > > > concept. Instead set it based on the optimal I/O size by lifting the > > > algorithm from the md driver when registering the disk. Also set > > > bdi->io_pages there as well by applying the same scheme based on > > > max_sectors. > > > > > > Signed-off-by: Christoph Hellwig <hch@xxxxxx> > > > --- > > > block/blk-settings.c | 5 ++--- > > > block/blk-sysfs.c | 1 - > > > block/genhd.c | 13 +++++++++++-- > > > drivers/block/aoe/aoeblk.c | 2 -- > > > drivers/block/drbd/drbd_nl.c | 12 +----------- > > > drivers/md/bcache/super.c | 4 ---- > > > drivers/md/dm-table.c | 3 --- > > > drivers/md/raid0.c | 16 ---------------- > > > drivers/md/raid10.c | 24 +----------------------- > > > drivers/md/raid5.c | 13 +------------ > > > 10 files changed, 16 insertions(+), 77 deletions(-) > > > > > > In general these changes need a solid audit relative to stacking > > drivers. That is, the limits stacking methods (blk_stack_limits) > > vs lower level allocation methods (__device_add_disk). > > > > You optimized for lowlevel __device_add_disk establishing the bdi's > > ra_pages and io_pages. That is at the beginning of disk allocation, > > well before any build up of stacking driver's queue_io_opt() -- which > > was previously done in disk_stack_limits or driver specific methods > > (e.g. dm_table_set_restrictions) that are called _after_ all the limits > > stacking occurs. > > > > By inverting the setting of the bdi's ra_pages and io_pages to be done > > so early in __device_add_disk it'll break properly setting these values > > for at least DM afaict. > > ra_pages never got inherited by stacking drivers, check it by modifying > it on an underlying device and then creating a trivial dm or md one. Sure, not saying that it did. But if the goal is to set ra_pages based on io_opt then to do that correctly on stacking drivers it must be done in terms of limits stacking right? Or at least done at a location that is after the limits stacking has occurred? So should DM just open-code setting ra_pages like it did for io_pages? Because setting ra_pages in __device_add_disk() is way too early for DM -- given it uses device_add_disk_no_queue_reg via add_disk_no_queue_reg at DM device creation (before stacking all underlying devices' limits). > And I think that is a good thing - in general we shouldn't really mess > with this thing from drivers if we can avoid it. I've kept the legacy > aoe and md parity raid cases, out of which the first looks pretty weird > and the md one at least remotely sensible. I don't want drivers, like DM, to have to worry about these. So I agree with that goal ;) > ->io_pages is still inherited in disk_stack_limits, just like before > so no change either. I'm missing where, but I only looked closer at this 06/14 patch. In it I see io_pages is no longer adjusted in disk_stack_limits(). Mike
