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dm thin: support discard with non power of two block size

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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 <snitzer@redhat.com>
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Mike Snitzer 2012-10-12 21:02:07 +01:00 committed by Alasdair G Kergon
parent 0bcf08798e
commit 28eed34e76
1 changed files with 13 additions and 10 deletions
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23
drivers/md/dm-thin.c
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@ -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)