[dm-devel] [PATCH] dm-kcopyd: avoid useless atomic operations

[Damien Le Moal]

On 2021/05/26 4:50, Mikulas Patocka wrote:
> The functions set_bit and clear_bit are atomic. We don't need atomicity
> when making flags for dm-kcopyd. So, change them to direct manipulation of
> the flags.
> 
> Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
> 
> Index: linux-2.6/drivers/md/dm-kcopyd.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm-kcopyd.c
> +++ linux-2.6/drivers/md/dm-kcopyd.c
> @@ -812,7 +812,7 @@ void dm_kcopyd_copy(struct dm_kcopyd_cli
>  	if (!test_bit(DM_KCOPYD_WRITE_SEQ, &job->flags)) {
>  		for (i = 0; i < job->num_dests; i++) {
>  			if (bdev_zoned_model(dests[i].bdev) == BLK_ZONED_HM) {
> -				set_bit(DM_KCOPYD_WRITE_SEQ, &job->flags);
> +				job->flags |= 1UL << DM_KCOPYD_WRITE_SEQ;

How about using the BIT() macro ?

job->flags |= BIT(DM_KCOPYD_WRITE_SEQ);

But I know some do not like that macro :)


>  				break;
>  			}
>  		}
> @@ -823,7 +823,7 @@ void dm_kcopyd_copy(struct dm_kcopyd_cli
>  	 */
>  	if (test_bit(DM_KCOPYD_WRITE_SEQ, &job->flags) &&
>  	    test_bit(DM_KCOPYD_IGNORE_ERROR, &job->flags))
> -		clear_bit(DM_KCOPYD_IGNORE_ERROR, &job->flags);
> +		job->flags &= ~(1UL << DM_KCOPYD_IGNORE_ERROR);
>  
>  	if (from) {
>  		job->source = *from;
> Index: linux-2.6/drivers/md/dm-raid1.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm-raid1.c
> +++ linux-2.6/drivers/md/dm-raid1.c
> @@ -364,7 +364,7 @@ static void recover(struct mirror_set *m
>  
>  	/* hand to kcopyd */
>  	if (!errors_handled(ms))
> -		set_bit(DM_KCOPYD_IGNORE_ERROR, &flags);
> +		flags |= 1UL << DM_KCOPYD_IGNORE_ERROR;
>  
>  	dm_kcopyd_copy(ms->kcopyd_client, &from, ms->nr_mirrors - 1, to,
>  		       flags, recovery_complete, reg);
> Index: linux-2.6/drivers/md/dm-zoned-reclaim.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm-zoned-reclaim.c
> +++ linux-2.6/drivers/md/dm-zoned-reclaim.c
> @@ -134,7 +134,7 @@ static int dmz_reclaim_copy(struct dmz_r
>  	dst_zone_block = dmz_start_block(zmd, dst_zone);
>  
>  	if (dmz_is_seq(dst_zone))
> -		set_bit(DM_KCOPYD_WRITE_SEQ, &flags);
> +		flags |= 1UL << DM_KCOPYD_WRITE_SEQ;
>  
>  	while (block < end_block) {
>  		if (src_zone->dev->flags & DMZ_BDEV_DYING)
> 
> --
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> dm-devel at redhat.com
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Either way, looks fine to me.

Reviewed-by: Damien Le Moal <damien.lemoal at wdc.com>


-- 
Damien Le Moal
Western Digital Research