[RFC PATCH 4/9] dm thin: update reserve space func to allow reduction

Brian Foster
2016-03-17T14:30:47Z

The dm-thin set_reserve_count() function is designed to control the
current block reservation for a thin pool. It currently only provides
the ability to increase the reservation.

Clients such as XFS will rely on over-reservation and thus require the
ability to release excess reservation back to the pool. Update
set_reserve_count() to return reserved blocks back to the pool.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
drivers/md/dm-thin.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 31d36da..ac770d89 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -1429,7 +1429,8 @@ static bool dec_reserve_count(struct thin_c *tc, dm_block_t free_blocks)
static int set_reserve_count(struct thin_c *tc, dm_block_t count)
{
int r;
- dm_block_t free_blocks, delta;
+ dm_block_t free_blocks;
+ int64_t delta;
unsigned long flags;

r = get_free_blocks(tc->pool, &free_blocks);
@@ -1437,8 +1438,6 @@ static int set_reserve_count(struct thin_c *tc, dm_block_t count)
return r;

spin_lock_irqsave(&tc->pool->lock, flags);
- if (count <= tc->reserve_count)
- goto out_unlock; /* nothing to do */
delta = count - tc->reserve_count;
if (tc->pool->reserve_count + delta > free_blocks)
r = -ENOSPC;
@@ -1446,7 +1445,6 @@ static int set_reserve_count(struct thin_c *tc, dm_block_t count)
tc->reserve_count = count;
tc->pool->reserve_count += delta;
}
-out_unlock:
spin_unlock_irqrestore(&tc->pool->lock, flags);

return r;
@@ -4369,7 +4367,7 @@ static int thin_reserve_space(struct dm_target *ti, sector_t nr_sects)
* @nr_sects must always be a factor of the pool's blocksize;
* upper layers can rely on the bdev's minimum_io_size for this.
*/
- if (!nr_sects || !is_factor(nr_sects, pool->sectors_per_block))
+ if (!is_factor(nr_sects, pool->sectors_per_block))
return -EINVAL;

blocks = nr_sects;