dm persistent data: remove space map ref_count entries if redundant

Save space by removing entries from the space map ref_count tree if
they're no longer needed.

Ref counts are stored in two places: a bitmap if the ref_count is
below 3, or a btree of uint32_t if 3 or above.

When a ref_count that was above 3 drops below we can remove it from
the tree and save some metadata space.  This removal was commented out
before because I was unsure why this was causing under-populated btree
nodes.  Earlier patches have fixed this issue.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

diff --git a/drivers/md/persistent-data/dm-space-map-common.c b/drivers/md/persistent-data/dm-space-map-common.c
index df2494c..ff3beed 100644 (file)
--- a/drivers/md/persistent-data/dm-space-map-common.c
+++ b/drivers/md/persistent-data/dm-space-map-common.c
@@ -405,8 +405,6 @@ int sm_ll_insert(struct ll_disk *ll, dm_block_t b,
                if (r < 0)
                        return r;
 
-#if 0
-               /* FIXME: dm_btree_remove doesn't handle this yet */
                if (old > 2) {
                        r = dm_btree_remove(&ll->ref_count_info,
                                            ll->ref_count_root,
@@ -414,7 +412,6 @@ int sm_ll_insert(struct ll_disk *ll, dm_block_t b,
                        if (r)
                                return r;
                }
-#endif
 
        } else {
                __le32 le_rc = cpu_to_le32(ref_count);