[dm-devel] [PATCH] dm-zoned: Avoid metadata flush writeback throttling

[Christoph Hellwig]

On Mon, Jul 24, 2017 at 04:44:22PM +0900, Damien Le Moal wrote:
> Avoid metadata flush to be blocked by the writeback throttling code in
> wbt_wait(). Otherwise, we can end up with a deadlock under heavy write
> load with all chunk works active. In such situation, a deadlock can
> happen if the flush work is blocked by the throttling code while holding
> the metadata lock: as the chunk works will wait for the metadata lock
> too, no progress can be made.
> 
> Signed-off-by: Damien Le Moal <damien.lemoal at wdc.com>
> ---
>  drivers/md/dm-zoned-metadata.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/md/dm-zoned-metadata.c b/drivers/md/dm-zoned-metadata.c
> index 884ff7c170a0..f694fb98b002 100644
> --- a/drivers/md/dm-zoned-metadata.c
> +++ b/drivers/md/dm-zoned-metadata.c
> @@ -567,7 +567,8 @@ static void dmz_write_mblock(struct dmz_metadata *zmd, struct dmz_mblock *mblk,
>  	bio->bi_bdev = zmd->dev->bdev;
>  	bio->bi_private = mblk;
>  	bio->bi_end_io = dmz_mblock_bio_end_io;
> -	bio_set_op_attrs(bio, REQ_OP_WRITE, REQ_META | REQ_PRIO);
> +	bio_set_op_attrs(bio, REQ_OP_WRITE,
> +			 REQ_META | REQ_PRIO | REQ_SYNC | REQ_IDLE);

Please just assign bi_opf directly instea dof using bio_set_op_attrs
in new code.

Also what do you need REQ_IDLE for?