dm persistent data: only commit space map if index changed

Introduce bitmap_index_changed to track whether or not the index changed
then only commit a space map if it did.

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>

2 files changed, 12 insertions, 1 deletions

diff --git a/drivers/md/persistent-data/dm-space-map-common.c b/drivers/md/persistent-data/dm-space-map-common.c
index ff3beed6ad2d..d77602d63c83 100644
--- a/drivers/md/persistent-data/dm-space-map-common.c
+++ b/drivers/md/persistent-data/dm-space-map-common.c
@@ -224,6 +224,7 @@ static int sm_ll_init(struct ll_disk *ll, struct dm_transaction_manager *tm)
         ll->nr_blocks = 0;
         ll->bitmap_root = 0;
         ll->ref_count_root = 0;
+        ll->bitmap_index_changed = false;
 
         return 0;
 }
@@ -476,7 +477,15 @@ int sm_ll_dec(struct ll_disk *ll, dm_block_t b, enum allocation_event *ev)
 
 int sm_ll_commit(struct ll_disk *ll)
 {
-        return ll->commit(ll);
+        int r = 0;
+
+        if (ll->bitmap_index_changed) {
+                r = ll->commit(ll);
+                if (!r)
+                        ll->bitmap_index_changed = false;
+        }
+
+        return r;
 }
 
 /*----------------------------------------------------------------*/
@@ -491,6 +500,7 @@ static int metadata_ll_load_ie(struct ll_disk *ll, dm_block_t index,
 static int metadata_ll_save_ie(struct ll_disk *ll, dm_block_t index,
                                struct disk_index_entry *ie)
 {
+        ll->bitmap_index_changed = true;
         memcpy(ll->mi_le.index + index, ie, sizeof(*ie));
         return 0;
 }
diff --git a/drivers/md/persistent-data/dm-space-map-common.h b/drivers/md/persistent-data/dm-space-map-common.h
index 8f220821a9a9..b3078d5eda0c 100644
--- a/drivers/md/persistent-data/dm-space-map-common.h
+++ b/drivers/md/persistent-data/dm-space-map-common.h
@@ -78,6 +78,7 @@ struct ll_disk {
         open_index_fn open_index;
         max_index_entries_fn max_entries;
         commit_fn commit;
+        bool bitmap_index_changed:1;
 };
 
 struct disk_sm_root {