[dm-devel] [Question] Why queue_work unneeded for REQUEUE bio

[JeffleXu]

Hi Mike,


I have another question about dm, though it's irrelevant to this original

mail.


Currently abnormal IO will call blk_queue_split() and normal IO will

be split considering @max_sectors/@chunk_sectos (in max_io_len()).


Question 1: Why bio should be split considering queue_limits in dm layer?

After all the underlying device will split themselves by queue_limits if

the dm layer doesn't split by queue_limits.


Then Question 2: Currently only @max_sectors is considered when splitting

normal IO in dm layer. Should we also consider 
@max_segments/@max_segment_size

as blk_queue_split() does?


Thanks,

Jeffle


On 11/3/20 5:23 PM, Jeffle Xu wrote:
> Hi Mike,
>
> Why queue_work() is unnecessary here for bio with BLK_STS_DM_REQUEUE
> returned?
>
> Thanks
> Jeffle Xu
>
> ---
>   drivers/md/dm.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index c18fc2548518..ae550daa99b5 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -908,9 +908,11 @@ static void dec_pending(struct dm_io *io, blk_status_t error)
>   			 * Target requested pushing back the I/O.
>   			 */
>   			spin_lock_irqsave(&md->deferred_lock, flags);
> -			if (__noflush_suspending(md))
> +			if (__noflush_suspending(md)) {
>   				/* NOTE early return due to BLK_STS_DM_REQUEUE below */
>   				bio_list_add_head(&md->deferred, io->orig_bio);
> +				queue_work(md->wq, &md->work);
> +			}
>   			else
>   				/* noflush suspend was interrupted. */
>   				io->status = BLK_STS_IOERR;

-- 
Thanks,
Jeffle