ddt: dedup table quota enforcement

This adds two new pool properties:
- dedup_table_size, the total size of all DDTs on the pool; and
- dedup_table_quota, the maximum possible size of all DDTs in the pool

When set, quota will be enforced by checking when a new entry is about
to be created. If the pool is over its dedup quota, the entry won't be
created, and the corresponding write will be converted to a regular
non-dedup write. Note that existing entries can be updated (ie their
refcounts changed), as that reuses the space rather than requiring more.

dedup_table_quota can be set to 'auto', which will set it based on the
size of the devices backing the "dedup" allocation device. This makes it
possible to limit the DDTs to the size of a dedup vdev only, such that
when the device fills, no new blocks are deduplicated.

Sponsored-by: iXsystems, Inc.
Sponsored-By: Klara Inc.
Reviewed-by: Alexander Motin <[email protected]>
Reviewed-by: Tony Hutter <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Rob Norris <[email protected]>
Signed-off-by: Don Brady <[email protected]>
Co-authored-by: Don Brady <[email protected]>
Co-authored-by: Rob Wing <[email protected]>
Co-authored-by: Sean Eric Fagan <[email protected]>
Closes #15889 

1 files changed, 7 insertions, 0 deletions

diff --git a/module/zfs/spa_misc.c b/module/zfs/spa_misc.c
index d1d41bbe7..439e56f0d 100644
--- a/module/zfs/spa_misc.c
+++ b/module/zfs/spa_misc.c
@@ -1996,6 +1996,13 @@ spa_dedup_class(spa_t *spa)
 	return (spa->spa_dedup_class);
 }
 
+boolean_t
+spa_special_has_ddt(spa_t *spa)
+{
+	return (zfs_ddt_data_is_special &&
+	    spa->spa_special_class->mc_groups != 0);
+}
+
 /*
  * Locate an appropriate allocation class
  */