# Re: \[PATCH 06/14\] block: lift setting the readahead size into the block layer

- From: Christoph Hellwig \<hch@lst.de\>
- Date: 2020-09-15 07:07:29 
- List: linux-raid
- Page: https://ratatoskr.run/linux-raid/2020/09/188635
- Thread: https://ratatoskr.run/linux-block/2020/07/185244/t.md

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