path: root/drivers/md
diff options
authorMike Snitzer <snitzer@redhat.com>2014-11-20 18:07:43 -0500
committerMike Snitzer <snitzer@redhat.com>2014-11-21 12:54:23 -0500
commitd200c30ef00dd03aec6f1aeaac1546c6e515cbc0 (patch)
treed88a4b7b8f924a81266307d4c1df6c07f18bc583 /drivers/md
parent583024d248f486e21479d1912aa2093565455770 (diff)
dm thin: fix pool_io_hints to avoid looking at max_hw_sectors
Simplify the pool_io_hints code that works to establish a max_sectors value that is a power-of-2 factor of the thin-pool's blocksize. The biggest associated improvement is that the DM thin-pool is no longer concerning itself with the data device's max_hw_sectors when adjusting max_sectors. This fixes the relative fragility of the original "dm thin: adjust max_sectors_kb based on thinp blocksize" commit that only became apparent when testing was performed using a DM thin-pool ontop of a virtio_blk device. One proposed upstream patch detailed the problems inherent in virtio_blk: https://lkml.org/lkml/2014/11/20/611 So even though virtio_blk incorrectly set its max_hw_sectors it actually helped make it clear that we need DM thinp to be tolerant of any future Linux driver that incorrectly sets max_hw_sectors. We only need to be concerned with modifying the thin-pool device's max_sectors limit if it is smaller than the thin-pool's blocksize. In this case the value of max_sectors does become a limiting factor when upper layers (e.g. filesystems) construct their bios. But if the hardware can support IOs larger than the thin-pool's blocksize the user is encouraged to adjust the thin-pool's data device's max_sectors accordingly -- doing so will enable the thin-pool to inherit the established user-defined max_sectors. Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Diffstat (limited to 'drivers/md')
1 files changed, 7 insertions, 14 deletions
diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index e9e9584fe769..8735543eacdb 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -3587,27 +3587,20 @@ static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)
sector_t io_opt_sectors = limits->io_opt >> SECTOR_SHIFT;
- * Adjust max_sectors_kb to highest possible power-of-2
- * factor of pool->sectors_per_block.
+ * If max_sectors is smaller than pool->sectors_per_block adjust it
+ * to the highest possible power-of-2 factor of pool->sectors_per_block.
+ * This is especially beneficial when the pool's data device is a RAID
+ * device that has a full stripe width that matches pool->sectors_per_block
+ * -- because even though partial RAID stripe-sized IOs will be issued to a
+ * single RAID stripe; when aggregated they will end on a full RAID stripe
+ * boundary.. which avoids additional partial RAID stripe writes cascading
- if (limits->max_hw_sectors & (limits->max_hw_sectors - 1))
- limits->max_sectors = rounddown_pow_of_two(limits->max_hw_sectors);
- else
- limits->max_sectors = limits->max_hw_sectors;
if (limits->max_sectors < pool->sectors_per_block) {
while (!is_factor(pool->sectors_per_block, limits->max_sectors)) {
if ((limits->max_sectors & (limits->max_sectors - 1)) == 0)
limits->max_sectors = rounddown_pow_of_two(limits->max_sectors);
- } else if (block_size_is_power_of_two(pool)) {
- /* max_sectors_kb is >= power-of-2 thinp blocksize */
- while (!is_factor(limits->max_sectors, pool->sectors_per_block)) {
- if ((limits->max_sectors & (limits->max_sectors - 1)) == 0)
- limits->max_sectors--;
- limits->max_sectors = rounddown_pow_of_two(limits->max_sectors);
- }

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