From: Yongpeng Yang <[email protected]> Currently, the max_hw_discard_sectors of a stripe target is set to the minimum max_hw_discard_sectors among all sub devices. When the discard bio is larger than max_hw_discard_sectors, this may cause the stripe device to split discard bios unnecessarily, because the value of max_hw_discard_sectors affects max_discard_sectors, which equal to min(max_hw_discard_sectors, max_user_discard_sectors).
For example: root@vm:~# echo '0 33554432 striped 2 256 /dev/vdd 0 /dev/vde 0' | dmsetup create stripe_dev root@vm:~# cat /sys/block/dm-1/queue/discard_max_bytes 536870912 root@vm:~# cat /sys/block/dm-1/slaves/vdd/queue/discard_max_bytes 536870912 root@vm:~# blkdiscard -o 0 -l 1073741824 -p 1073741824 /dev/mapper/stripe_dev dm-1 is the stripe device, and its discard_max_bytes is equal to each sub device’s discard_max_bytes. Since the requested discard length exceeds discard_max_bytes, the block layer splits the discard bio: block_bio_queue: 252,1 DS 0 + 2097152 [blkdiscard] block_split: 252,1 DS 0 / 1048576 [blkdiscard] block_rq_issue: 253,48 DS 268435456 () 0 + 524288 be,0,4 [blkdiscard] block_bio_queue: 253,64 DS 524288 + 524288 [blkdiscard] However, both vdd and vde can actually handle a discard bio of 536870912 bytes, so this split is not necessary. This patch updates the stripe target’s q->limits.max_hw_discard_sectors to be the minimum max_hw_discard_sectors of the sub devices multiplied by the # of stripe devices, and max_hw_discard_sectors must round down to chunk size multiply # of stripe devices to avoid issue discard bio to sub devices which is larger than max_hw_discard_sectors. This patch enables the stripe device to handle larger discard bios without incurring unnecessary splitting. Signed-off-by: Yongpeng Yang <[email protected]> --- v3: - Rounding stipe device's max_hw_discard_sectors down to a multiple of chunk_size. - Drop sc->max_discard_sectors code. v2: - When an overflow occurs, assign (UINT_MAX >> SECTOR_SHIFT) to limits->max_hw_discard_sectors. --- drivers/md/dm-stripe.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/drivers/md/dm-stripe.c b/drivers/md/dm-stripe.c index 1461dc740dae..8a872f5d633e 100644 --- a/drivers/md/dm-stripe.c +++ b/drivers/md/dm-stripe.c @@ -456,7 +456,7 @@ static void stripe_io_hints(struct dm_target *ti, struct queue_limits *limits) { struct stripe_c *sc = ti->private; - unsigned int io_min, io_opt; + unsigned int io_min, io_opt, max_hw_discard_sectors = limits->max_hw_discard_sectors; limits->chunk_sectors = sc->chunk_size; @@ -465,6 +465,14 @@ static void stripe_io_hints(struct dm_target *ti, limits->io_min = io_min; limits->io_opt = io_opt; } + if (max_hw_discard_sectors >= sc->chunk_size) { + if (!check_mul_overflow(max_hw_discard_sectors, sc->stripes, &max_hw_discard_sectors)) { + max_hw_discard_sectors = rounddown(max_hw_discard_sectors, + sc->chunk_size * sc->stripes); + limits->max_hw_discard_sectors = max_hw_discard_sectors; + } else + limits->max_hw_discard_sectors = UINT_MAX >> SECTOR_SHIFT; + } } static struct target_type stripe_target = { -- 2.43.0
