Christoph,
> Commit 16d80c54ad42 ("rbd: set io_min, io_opt and discard_granularity
> to alloc_size") lowered the io_opt size for rbd from objset_bytes
> which is 4MB for typical setup to alloc_size which is typically 64KB.
>
> The commit mostly talks about discard behavior and does mention io_min
> in passing. Reducing io_opt means reducing the readahead size, which
> seems counter-intuitive given that rbd currently abuses the user
> max_sectors setting to actually increase the I/O size. Switch back to
> the old setting to allow larger reads (the readahead size despite it's
> name actually limits the size of any buffered read) and to prepare for
> using io_opt in the max_sectors calculation and getting drivers out of
> the business of overriding the max_user_sectors value.
Reviewed-by: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
--
Martin K. Petersen Oracle Linux Engineering
