On Thu, Sep 10, 2020 at 01:15:41PM -0400, Mike Snitzer wrote:

quoted

I'll move it to blk_register_queue, which should work just fine.

That'll work for initial DM table load as part of DM device creation
(dm_setup_md_queue).  But it won't account for DM table reloads that
might change underlying devices on a live DM device (done using
__bind).

Both dm_setup_md_queue() and __bind() call dm_table_set_restrictions()
to set/update queue_limits.  It feels like __bind() will need to call a
new block helper to set/update parts of queue_limits (e.g. ra_pages and
io_pages).

Any chance you're open to factoring out that block function as an
exported symbol for use by blk_register_queue() and code like DM's
__bind()?

I agree with the problem statement.  OTOH adding an exported helper
for two trivial assignments seems a little silly..

For now I'll just keep the open coded ->io_pages assignment in
dm.  Note that dm doesn't currently update the ->ra_pages value
based on the underlying devices, so an incremental patch to do that
might be useful as well.