On Fri, Dec 04 2020 at 12:32P -0500, Mike Snitzer <snitzer@xxxxxxxxxx> wrote: > 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))) FYI, above blkdev.h diff missed this hunk: @@ -1101,7 +1102,7 @@ static inline unsigned int blk_rq_get_max_sectors(struct request *rq, req_op(rq) == REQ_OP_SECURE_ERASE) return blk_queue_get_max_sectors(q, req_op(rq)); - return min(blk_max_size_offset(q, offset), + return min(blk_max_size_offset(q, offset, 0), blk_queue_get_max_sectors(q, req_op(rq))); }
