[dm-devel] [PATCH] dm thin: set {minimum, optimal}_io_size to pool's data block size

Mike Snitzer snitzer at redhat.com
Fri Jul 18 21:59:43 UTC 2014

Before if the block layer's limit stacking didn't establish an
optimal_io_size that was compatible with the dm-thin-pool's data block
size of the we'd set optimal_io_size to the data block size and
minimum_io_size to 0 (which the block layer adjusts to be

Update pool_io_hints() to set both minimum_io_size and optimal_io_size
to the pool's data block size.  This fixes an issue reported where
mkfs.xfs would create more XFS Allocation Groups on thinp volumes than
on a normal linear LV of comparable size, see:

Reported-by: Chris Murphy <lists at colorremedies.com>
Signed-off-by: Mike Snitzer <snitzer at redhat.com>
 drivers/md/dm-thin.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index fc9c848..c92e1b9 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -3112,7 +3112,7 @@ static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)
 	if (io_opt_sectors < pool->sectors_per_block ||
 	    do_div(io_opt_sectors, pool->sectors_per_block)) {
-		blk_limits_io_min(limits, 0);
+		blk_limits_io_min(limits, pool->sectors_per_block << SECTOR_SHIFT);
 		blk_limits_io_opt(limits, pool->sectors_per_block << SECTOR_SHIFT);

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