On Fri, May 31, 2024 at 9:48 AM Christoph Hellwig <hch@xxxxxx> wrote:
>
> 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.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> drivers/block/rbd.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
> index 26ff5cd2bf0abc..46dc487ccc17eb 100644
> --- a/drivers/block/rbd.c
> +++ b/drivers/block/rbd.c
> @@ -4955,8 +4955,8 @@ static int rbd_init_disk(struct rbd_device *rbd_dev)
> struct queue_limits lim = {
> .max_hw_sectors = objset_bytes >> SECTOR_SHIFT,
> .max_user_sectors = objset_bytes >> SECTOR_SHIFT,
> + .io_opt = objset_bytes,
> .io_min = rbd_dev->opts->alloc_size,
> - .io_opt = rbd_dev->opts->alloc_size,
> .max_segments = USHRT_MAX,
> .max_segment_size = UINT_MAX,
> };
> --
> 2.43.0
>
Acked-by: Ilya Dryomov <idryomov@xxxxxxxxx>
Thanks,
Ilya
