On Wed, Sep 02, 2020 at 12:20:07PM -0400, Mike Snitzer wrote:
On Wed, Sep 02 2020 at 11:11am -0400,
Christoph Hellwig [off-list ref] wrote:
quoted
On Wed, Aug 26, 2020 at 06:07:38PM -0400, Mike Snitzer wrote:
quoted
On Sun, Jul 26 2020 at 11:03am -0400,
Christoph Hellwig [off-list ref] wrote:
quoted
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@lst.de>
---
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).
I'll move it to blk_register_queue, which should work just fine.