1 files changed, 45 insertions, 7 deletions

diff --git a/fs/btrfs/discard.c b/fs/btrfs/discard.c
index ee5f5b2788e1..1c304bf473e5 100644
--- a/fs/btrfs/discard.c
+++ b/fs/btrfs/discard.c
@@ -216,6 +216,25 @@ static struct btrfs_block_group *find_next_block_group(
 }
 
 /*
+ * Check whether a block group is empty.
+ *
+ * "Empty" here means that there are no extents physically located within the
+ * device extents corresponding to this block group.
+ *
+ * For a remapped block group, this means that all of its identity remaps have
+ * been removed. For a non-remapped block group, this means that no extents
+ * have an address within its range, and that nothing has been remapped to be
+ * within it.
+ */
+static bool block_group_is_empty(const struct btrfs_block_group *bg)
+{
+	if (bg->flags & BTRFS_BLOCK_GROUP_REMAPPED)
+		return bg->identity_remap_count == 0;
+
+	return bg->used == 0 && bg->remap_bytes == 0;
+}
+
+/*
  * Look up next block group and set it for use.
  *
  * @discard_ctl:   discard control
@@ -241,8 +260,10 @@ again:
 	block_group = find_next_block_group(discard_ctl, now);
 
 	if (block_group && now >= block_group->discard_eligible_time) {
+		const bool empty = block_group_is_empty(block_group);
+
 		if (block_group->discard_index == BTRFS_DISCARD_INDEX_UNUSED &&
-		    block_group->used != 0) {
+		    !empty) {
 			if (btrfs_is_block_group_data_only(block_group)) {
 				__add_to_discard_list(discard_ctl, block_group);
 				/*
@@ -267,7 +288,12 @@ again:
 		}
 		if (block_group->discard_state == BTRFS_DISCARD_RESET_CURSOR) {
 			block_group->discard_cursor = block_group->start;
-			block_group->discard_state = BTRFS_DISCARD_EXTENTS;
+
+			if (block_group->flags & BTRFS_BLOCK_GROUP_REMAPPED && empty) {
+				block_group->discard_state = BTRFS_DISCARD_FULLY_REMAPPED;
+			} else {
+				block_group->discard_state = BTRFS_DISCARD_EXTENTS;
+			}
 		}
 	}
 	if (block_group) {
@@ -373,7 +399,7 @@ void btrfs_discard_queue_work(struct btrfs_discard_ctl *discard_ctl,
 	if (!block_group || !btrfs_test_opt(block_group->fs_info, DISCARD_ASYNC))
 		return;
 
-	if (block_group->used == 0 && block_group->remap_bytes == 0)
+	if (block_group_is_empty(block_group))
 		add_to_discard_unused_list(discard_ctl, block_group);
 	else
 		add_to_discard_list(discard_ctl, block_group);
@@ -470,7 +496,7 @@ static void btrfs_finish_discard_pass(struct btrfs_discard_ctl *discard_ctl,
 {
 	remove_from_discard_list(discard_ctl, block_group);
 
-	if (block_group->used == 0) {
+	if (block_group_is_empty(block_group)) {
 		if (btrfs_is_free_space_trimmed(block_group))
 			btrfs_mark_bg_unused(block_group);
 		else
@@ -524,7 +550,8 @@ static void btrfs_discard_workfn(struct work_struct *work)
 	/* Perform discarding */
 	minlen = discard_minlen[discard_index];
 
-	if (discard_state == BTRFS_DISCARD_BITMAPS) {
+	switch (discard_state) {
+	case BTRFS_DISCARD_BITMAPS: {
 		u64 maxlen = 0;
 
 		/*
@@ -541,17 +568,28 @@ static void btrfs_discard_workfn(struct work_struct *work)
 				       btrfs_block_group_end(block_group),
 				       minlen, maxlen, true);
 		discard_ctl->discard_bitmap_bytes += trimmed;
-	} else {
+
+		break;
+	}
+
+	case BTRFS_DISCARD_FULLY_REMAPPED:
+		btrfs_trim_fully_remapped_block_group(block_group);
+		break;
+
+	default:
 		btrfs_trim_block_group_extents(block_group, &trimmed,
 				       block_group->discard_cursor,
 				       btrfs_block_group_end(block_group),
 				       minlen, true);
 		discard_ctl->discard_extent_bytes += trimmed;
+
+		break;
 	}
 
 	/* Determine next steps for a block_group */
 	if (block_group->discard_cursor >= btrfs_block_group_end(block_group)) {
-		if (discard_state == BTRFS_DISCARD_BITMAPS) {
+		if (discard_state == BTRFS_DISCARD_BITMAPS ||
+		    discard_state == BTRFS_DISCARD_FULLY_REMAPPED) {
 			btrfs_finish_discard_pass(discard_ctl, block_group);
 		} else {
 			block_group->discard_cursor = block_group->start;