On Fri, Dec 04 2020 at 11:47P -0500, Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > On Thu, Dec 03 2020 at 10:59pm -0500, > Ming Lei <ming.lei@xxxxxxxxxx> wrote: > > > On Thu, Dec 03, 2020 at 09:03:43PM -0500, Mike Snitzer wrote: > > > Stacking chunk_sectors seems ill-conceived. One size-fits-all splitting > > > is too rigid. > > > > DM/VDO knows exactly it is one hard chunk_sectors limit, and DM shouldn't play > > the stacking trick on VDO's chunk_sectors limit, should it? > > Feel like I already answered this in detail but... correct, DM cannot > and should not use stacked chunk_sectors as basis for splitting. > > Up until 5.9, where I changed DM core to set and then use chunk_sectors > for splitting via blk_max_size_offset(), DM only used its own per-target > ti->max_io_len in drivers/md/dm.c:max_io_len(). > > But I reverted back to DM's pre-5.9 splitting in this stable@ fix that > I'll be sending to Linus today for 5.10-rcX: > https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-5.10-rcX&id=6bb38bcc33bf3093c08bd1b71e4f20c82bb60dd1 > > DM is now back to pre-5.9 behavior where it doesn't even consider > chunk_sectors for splitting (NOTE: dm-zoned sets ti->max_io_len though > so it is effectively achieves the same boundary splits via max_io_len). Last question for all, I'd be fine with the following fix instead of the above referenced commit 6bb38bcc33. It'd allow DM to continue to use blk_max_size_offset(), any opinions? From: Mike Snitzer <snitzer@xxxxxxxxxx> Date: Fri, 4 Dec 2020 12:03:25 -0500 Subject: [RFC PATCH] dm: fix IO splitting FIXME: add proper header Add chunk_sectors override to blk_max_size_offset(). Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx> --- block/blk-merge.c | 2 +- drivers/md/dm-table.c | 5 ----- drivers/md/dm.c | 19 +++++++++++-------- include/linux/blkdev.h | 9 +++++---- 4 files changed, 17 insertions(+), 18 deletions(-) diff --git a/block/blk-merge.c b/block/blk-merge.c index bcf5e4580603..97b7c2821565 100644 --- a/block/blk-merge.c +++ b/block/blk-merge.c @@ -144,7 +144,7 @@ static struct bio *blk_bio_write_same_split(struct request_queue *q, static inline unsigned get_max_io_size(struct request_queue *q, struct bio *bio) { - unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector); + unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector, 0); unsigned max_sectors = sectors; unsigned pbs = queue_physical_block_size(q) >> SECTOR_SHIFT; unsigned lbs = queue_logical_block_size(q) >> SECTOR_SHIFT; diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c index 2073ee8d18f4..7eeb7c4169c9 100644 --- a/drivers/md/dm-table.c +++ b/drivers/md/dm-table.c @@ -18,7 +18,6 @@ #include <linux/mutex.h> #include <linux/delay.h> #include <linux/atomic.h> -#include <linux/lcm.h> #include <linux/blk-mq.h> #include <linux/mount.h> #include <linux/dax.h> @@ -1449,10 +1448,6 @@ int dm_calculate_queue_limits(struct dm_table *table, zone_sectors = ti_limits.chunk_sectors; } - /* Stack chunk_sectors if target-specific splitting is required */ - if (ti->max_io_len) - ti_limits.chunk_sectors = lcm_not_zero(ti->max_io_len, - ti_limits.chunk_sectors); /* Set I/O hints portion of queue limits */ if (ti->type->io_hints) ti->type->io_hints(ti, &ti_limits); diff --git a/drivers/md/dm.c b/drivers/md/dm.c index 98866e725f25..f7eb3d2964f3 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -1039,15 +1039,18 @@ static sector_t max_io_len(struct dm_target *ti, sector_t sector) sector_t max_len; /* - * Does the target need to split even further? - * - q->limits.chunk_sectors reflects ti->max_io_len so - * blk_max_size_offset() provides required splitting. - * - blk_max_size_offset() also respects q->limits.max_sectors + * Does the target need to split IO even further? + * - varied (per target) IO splitting is a tenet of DM; this + * explains why stacked chunk_sectors based splitting via + * blk_max_size_offset() isn't possible here. So pass in + * ti->max_io_len to override stacked chunk_sectors. */ - max_len = blk_max_size_offset(ti->table->md->queue, - target_offset); - if (len > max_len) - len = max_len; + if (ti->max_io_len) { + max_len = blk_max_size_offset(ti->table->md->queue, + target_offset, ti->max_io_len); + if (len > max_len) + len = max_len; + } return len; } diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index 639cae2c158b..f56dc5497e67 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -1073,11 +1073,12 @@ static inline unsigned int blk_queue_get_max_sectors(struct request_queue *q, * file system requests. */ static inline unsigned int blk_max_size_offset(struct request_queue *q, - sector_t offset) + sector_t offset, + unsigned int chunk_sectors) { - unsigned int chunk_sectors = q->limits.chunk_sectors; - - if (!chunk_sectors) + if (!chunk_sectors && q->limits.chunk_sectors) + chunk_sectors = q->limits.chunk_sectors; + else return q->limits.max_sectors; if (likely(is_power_of_2(chunk_sectors)))
