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authorMike Snitzer <snitzer@redhat.com>2020-11-30 10:57:43 -0500
committerMike Snitzer <snitzer@redhat.com>2020-12-04 14:53:15 -0500
commit3ee16db390b42b8a21f2ad2ea2518f3469c6e532 (patch)
tree2a34d72f6ef06b6708c8ae56577baa2c9506002b /drivers/md/dm.c
parent857c4c0a8b2888d806f4308c58f59a6a81a1dee9 (diff)
dm: fix IO splitting
Commit 882ec4e609c1 ("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 5091cdec56fa ("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: 882ec4e609c1 ("dm table: stack 'chunk_sectors' limit to account for target-specific splitting") Fixes: 5091cdec56fa ("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>
Diffstat (limited to 'drivers/md/dm.c')
-rw-r--r--drivers/md/dm.c19
1 files changed, 11 insertions, 8 deletions
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;
}