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dm: fix IO splitting

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Commit 882ec4e609 ("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 commit 5091cdec56 ("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>
This commit is contained in:
Mike Snitzer
2020-11-30 10:57:43 -05:00
parent 857c4c0a8b
commit 3ee16db390
4 changed files with 18 additions and 19 deletions
Download Patch File Download Diff File Expand all files Collapse all files

11
include/linux/blkdev.h
View File

@@ -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)))
@@ -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)));
}