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dm: fix IO splitting
Commit882ec4e609
("dm table: stack 'chunk_sectors' limit to account for target-specific splitting") caused a couple regressions: 1) Using lcm_not_zero() when stacking chunk_sectors was a bug because chunk_sectors must reflect the most limited of all devices in the IO stack. 2) DM targets that set max_io_len but that do _not_ provide an .iterate_devices method no longer had there IO split properly. And commit5091cdec56
("dm: change max_io_len() to use blk_max_size_offset()") also caused a regression where DM no longer supported varied (per target) IO splitting. The implication being the potential for severely reduced performance for IO stacks that use a DM target like dm-cache to hide performance limitations of a slower device (e.g. one that requires 4K IO splitting). Coming full circle: Fix all these issues by discontinuing stacking chunk_sectors up using ti->max_io_len in dm_calculate_queue_limits(), add optional chunk_sectors override argument to blk_max_size_offset() and update DM's max_io_len() to pass ti->max_io_len to its blk_max_size_offset() call. Passing in an optional chunk_sectors override to blk_max_size_offset() allows for code reuse of block's centralized calculation for max IO size based on provided offset and split boundary. Fixes:882ec4e609
("dm table: stack 'chunk_sectors' limit to account for target-specific splitting") Fixes:5091cdec56
("dm: change max_io_len() to use blk_max_size_offset()") Cc: stable@vger.kernel.org Reported-by: John Dorminy <jdorminy@redhat.com> Reported-by: Bruce Johnston <bjohnsto@redhat.com> Reported-by: Kirill Tkhai <ktkhai@virtuozzo.com> Reviewed-by: John Dorminy <jdorminy@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Reviewed-by: Jens Axboe <axboe@kernel.dk>
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parent
857c4c0a8b
commit
3ee16db390
4 changed files with 18 additions and 19 deletions
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@ -144,7 +144,7 @@ static struct bio *blk_bio_write_same_split(struct request_queue *q,
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static inline unsigned get_max_io_size(struct request_queue *q,
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struct bio *bio)
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{
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unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector);
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unsigned sectors = blk_max_size_offset(q, bio->bi_iter.bi_sector, 0);
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unsigned max_sectors = sectors;
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unsigned pbs = queue_physical_block_size(q) >> SECTOR_SHIFT;
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unsigned lbs = queue_logical_block_size(q) >> SECTOR_SHIFT;
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@ -18,7 +18,6 @@
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#include <linux/mutex.h>
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#include <linux/delay.h>
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#include <linux/atomic.h>
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#include <linux/lcm.h>
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#include <linux/blk-mq.h>
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#include <linux/mount.h>
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#include <linux/dax.h>
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@ -1449,10 +1448,6 @@ int dm_calculate_queue_limits(struct dm_table *table,
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zone_sectors = ti_limits.chunk_sectors;
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}
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/* Stack chunk_sectors if target-specific splitting is required */
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if (ti->max_io_len)
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ti_limits.chunk_sectors = lcm_not_zero(ti->max_io_len,
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ti_limits.chunk_sectors);
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/* Set I/O hints portion of queue limits */
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if (ti->type->io_hints)
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ti->type->io_hints(ti, &ti_limits);
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@ -1039,15 +1039,18 @@ static sector_t max_io_len(struct dm_target *ti, sector_t sector)
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sector_t max_len;
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/*
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* Does the target need to split even further?
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* - q->limits.chunk_sectors reflects ti->max_io_len so
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* blk_max_size_offset() provides required splitting.
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* - blk_max_size_offset() also respects q->limits.max_sectors
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* Does the target need to split IO even further?
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* - varied (per target) IO splitting is a tenet of DM; this
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* explains why stacked chunk_sectors based splitting via
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* blk_max_size_offset() isn't possible here. So pass in
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* ti->max_io_len to override stacked chunk_sectors.
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*/
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max_len = blk_max_size_offset(ti->table->md->queue,
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target_offset);
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if (len > max_len)
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len = max_len;
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if (ti->max_io_len) {
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max_len = blk_max_size_offset(ti->table->md->queue,
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target_offset, ti->max_io_len);
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if (len > max_len)
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len = max_len;
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}
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return len;
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}
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@ -1073,11 +1073,12 @@ static inline unsigned int blk_queue_get_max_sectors(struct request_queue *q,
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* file system requests.
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*/
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static inline unsigned int blk_max_size_offset(struct request_queue *q,
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sector_t offset)
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sector_t offset,
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unsigned int chunk_sectors)
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{
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unsigned int chunk_sectors = q->limits.chunk_sectors;
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if (!chunk_sectors)
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if (!chunk_sectors && q->limits.chunk_sectors)
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chunk_sectors = q->limits.chunk_sectors;
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else
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return q->limits.max_sectors;
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if (likely(is_power_of_2(chunk_sectors)))
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@ -1101,7 +1102,7 @@ static inline unsigned int blk_rq_get_max_sectors(struct request *rq,
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req_op(rq) == REQ_OP_SECURE_ERASE)
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return blk_queue_get_max_sectors(q, req_op(rq));
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return min(blk_max_size_offset(q, offset),
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return min(blk_max_size_offset(q, offset, 0),
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blk_queue_get_max_sectors(q, req_op(rq)));
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}
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