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Commit 28eed34e authored by Mike Snitzer's avatar Mike Snitzer Committed by Alasdair G Kergon
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dm thin: support discard with non power of two block size 



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
55f2b8bd ("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: default avatarMike Snitzer <snitzer@redhat.com>
Signed-off-by: default avatarJoe Thornber <ejt@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent 0bcf0879

drivers/md/dm-thin.c

+13 −10
Original line number Diff line number Diff line
@@ -2272,15 +2272,6 @@ static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv) 
		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 *ti, struct bvec_merge_data *bvm, 
	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 pool_c *pt, struct queue_limits *limits) 
	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)