From: Mike Snitzer Support discards when the pool's block size is not a power of 2. The block layer assumes discard_granularity is a power of 2 (in blkdev_issue_discard), so we set this to the largest power of 2 that is a divides into the number of sectors in each block, but never less than DATA_DEV_BLOCK_SIZE_MIN_SECTORS. This patch eliminates the "Discard support must be disabled when the block size is not a power of 2" constraint that was imposed in commit 55f2b8b ("dm thin: support for non power of 2 pool blocksize"). That commit was incomplete: using a block size that is not a power of 2 shouldn't mean disabling discard support on the device completely. Signed-off-by: Mike Snitzer Signed-off-by: Joe Thornber Signed-off-by: Alasdair G Kergon --- drivers/md/dm-thin.c | 23 +++++++++++++---------- 1 file changed, 13 insertions(+), 10 deletions(-) Index: linux/drivers/md/dm-thin.c =================================================================== --- linux.orig/drivers/md/dm-thin.c +++ linux/drivers/md/dm-thin.c @@ -2272,15 +2272,6 @@ static int pool_ctr(struct dm_target *ti goto out_flags_changed; } - /* - * The block layer requires discard_granularity to be a power of 2. - */ - if (pf.discard_enabled && !is_power_of_2(block_size)) { - ti->error = "Discard support must be disabled when the block size is not a power of 2"; - r = -EINVAL; - goto out_flags_changed; - } - pt->pool = pool; pt->ti = ti; pt->metadata_dev = metadata_dev; @@ -2762,6 +2753,11 @@ static int pool_merge(struct dm_target * return min(max_size, q->merge_bvec_fn(q, bvm, biovec)); } +static bool block_size_is_power_of_two(struct pool *pool) +{ + return pool->sectors_per_block_shift >= 0; +} + static void set_discard_limits(struct pool_c *pt, struct queue_limits *limits) { struct pool *pool = pt->pool; @@ -2775,8 +2771,15 @@ static void set_discard_limits(struct po if (pt->adjusted_pf.discard_passdown) { data_limits = &bdev_get_queue(pt->data_dev->bdev)->limits; limits->discard_granularity = data_limits->discard_granularity; - } else + } else if (block_size_is_power_of_two(pool)) limits->discard_granularity = pool->sectors_per_block << SECTOR_SHIFT; + else + /* + * Use largest power of 2 that is a factor of sectors_per_block + * but at least DATA_DEV_BLOCK_SIZE_MIN_SECTORS. + */ + limits->discard_granularity = max(1 << (ffs(pool->sectors_per_block) - 1), + DATA_DEV_BLOCK_SIZE_MIN_SECTORS) << SECTOR_SHIFT; } static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)