diff --git a/fs/btrfs/accessors.h b/fs/btrfs/accessors.h
index 09cdd6bfddf5..9797f9e8d4e5 100644
--- a/fs/btrfs/accessors.h
+++ b/fs/btrfs/accessors.h
@@ -240,6 +240,26 @@ BTRFS_SETGET_FUNCS(block_group_flags, struct btrfs_block_group_item, flags, 64);
 BTRFS_SETGET_STACK_FUNCS(stack_block_group_flags,
 			struct btrfs_block_group_item, flags, 64);
 
+/* struct btrfs_block_group_item_v2 */
+BTRFS_SETGET_STACK_FUNCS(stack_block_group_v2_used, struct btrfs_block_group_item_v2,
+			 used, 64);
+BTRFS_SETGET_FUNCS(block_group_v2_used, struct btrfs_block_group_item_v2, used, 64);
+BTRFS_SETGET_STACK_FUNCS(stack_block_group_v2_chunk_objectid,
+			 struct btrfs_block_group_item_v2, chunk_objectid, 64);
+BTRFS_SETGET_FUNCS(block_group_v2_chunk_objectid,
+		   struct btrfs_block_group_item_v2, chunk_objectid, 64);
+BTRFS_SETGET_STACK_FUNCS(stack_block_group_v2_flags,
+			 struct btrfs_block_group_item_v2, flags, 64);
+BTRFS_SETGET_FUNCS(block_group_v2_flags, struct btrfs_block_group_item_v2, flags, 64);
+BTRFS_SETGET_STACK_FUNCS(stack_block_group_v2_remap_bytes,
+			 struct btrfs_block_group_item_v2, remap_bytes, 64);
+BTRFS_SETGET_FUNCS(block_group_v2_remap_bytes, struct btrfs_block_group_item_v2,
+		   remap_bytes, 64);
+BTRFS_SETGET_STACK_FUNCS(stack_block_group_v2_identity_remap_count,
+			 struct btrfs_block_group_item_v2, identity_remap_count, 32);
+BTRFS_SETGET_FUNCS(block_group_v2_identity_remap_count, struct btrfs_block_group_item_v2,
+		   identity_remap_count, 32);
+
 /* struct btrfs_free_space_info */
 BTRFS_SETGET_FUNCS(free_space_extent_count, struct btrfs_free_space_info,
 		   extent_count, 32);
diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 5709acc84297..a1ab513fa8ea 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -2371,7 +2371,7 @@ static int check_chunk_block_group_mappings(struct btrfs_fs_info *fs_info)
 }
 
 static int read_one_block_group(struct btrfs_fs_info *info,
-				struct btrfs_block_group_item *bgi,
+				struct btrfs_block_group_item_v2 *bgi,
 				const struct btrfs_key *key,
 				int need_clear)
 {
@@ -2386,11 +2386,15 @@ static int read_one_block_group(struct btrfs_fs_info *info,
 		return -ENOMEM;
 
 	cache->length = key->offset;
-	cache->used = btrfs_stack_block_group_used(bgi);
+	cache->used = btrfs_stack_block_group_v2_used(bgi);
 	cache->last_used = cache->used;
-	cache->flags = btrfs_stack_block_group_flags(bgi);
-	cache->global_root_id = btrfs_stack_block_group_chunk_objectid(bgi);
+	cache->flags = btrfs_stack_block_group_v2_flags(bgi);
+	cache->global_root_id = btrfs_stack_block_group_v2_chunk_objectid(bgi);
 	cache->space_info = btrfs_find_space_info(info, cache->flags);
+	cache->remap_bytes = btrfs_stack_block_group_v2_remap_bytes(bgi);
+	cache->last_remap_bytes = cache->remap_bytes;
+	cache->identity_remap_count = btrfs_stack_block_group_v2_identity_remap_count(bgi);
+	cache->last_identity_remap_count = cache->identity_remap_count;
 
 	btrfs_set_free_space_tree_thresholds(cache);
 
@@ -2455,7 +2459,7 @@ static int read_one_block_group(struct btrfs_fs_info *info,
 	} else if (cache->length == cache->used) {
 		cache->cached = BTRFS_CACHE_FINISHED;
 		btrfs_free_excluded_extents(cache);
-	} else if (cache->used == 0) {
+	} else if (cache->used == 0 && cache->remap_bytes == 0) {
 		cache->cached = BTRFS_CACHE_FINISHED;
 		ret = btrfs_add_new_free_space(cache, cache->start,
 					       cache->start + cache->length, NULL);
@@ -2475,7 +2479,7 @@ static int read_one_block_group(struct btrfs_fs_info *info,
 
 	set_avail_alloc_bits(info, cache->flags);
 	if (btrfs_chunk_writeable(info, cache->start)) {
-		if (cache->used == 0) {
+		if (cache->used == 0 && cache->remap_bytes == 0) {
 			ASSERT(list_empty(&cache->bg_list));
 			if (btrfs_test_opt(info, DISCARD_ASYNC))
 				btrfs_discard_queue_work(&info->discard_ctl, cache);
@@ -2579,9 +2583,10 @@ int btrfs_read_block_groups(struct btrfs_fs_info *info)
 		need_clear = 1;
 
 	while (1) {
-		struct btrfs_block_group_item bgi;
+		struct btrfs_block_group_item_v2 bgi;
 		struct extent_buffer *leaf;
 		int slot;
+		size_t size;
 
 		ret = find_first_block_group(info, path, &key);
 		if (ret > 0)
@@ -2592,8 +2597,16 @@ int btrfs_read_block_groups(struct btrfs_fs_info *info)
 		leaf = path->nodes[0];
 		slot = path->slots[0];
 
+		if (btrfs_fs_incompat(info, REMAP_TREE)) {
+			size = sizeof(struct btrfs_block_group_item_v2);
+		} else {
+			size = sizeof(struct btrfs_block_group_item);
+			btrfs_set_stack_block_group_v2_remap_bytes(&bgi, 0);
+			btrfs_set_stack_block_group_v2_identity_remap_count(&bgi, 0);
+		}
+
 		read_extent_buffer(leaf, &bgi, btrfs_item_ptr_offset(leaf, slot),
-				   sizeof(bgi));
+				   size);
 
 		btrfs_item_key_to_cpu(leaf, &key, slot);
 		btrfs_release_path(path);
@@ -2663,25 +2676,34 @@ static int insert_block_group_item(struct btrfs_trans_handle *trans,
 				   struct btrfs_block_group *block_group)
 {
 	struct btrfs_fs_info *fs_info = trans->fs_info;
-	struct btrfs_block_group_item bgi;
+	struct btrfs_block_group_item_v2 bgi;
 	struct btrfs_root *root = btrfs_block_group_root(fs_info);
 	struct btrfs_key key;
 	u64 old_last_used;
+	size_t size;
 	int ret;
 
 	spin_lock(&block_group->lock);
-	btrfs_set_stack_block_group_used(&bgi, block_group->used);
-	btrfs_set_stack_block_group_chunk_objectid(&bgi,
-						   block_group->global_root_id);
-	btrfs_set_stack_block_group_flags(&bgi, block_group->flags);
+	btrfs_set_stack_block_group_v2_used(&bgi, block_group->used);
+	btrfs_set_stack_block_group_v2_chunk_objectid(&bgi, block_group->global_root_id);
+	btrfs_set_stack_block_group_v2_flags(&bgi, block_group->flags);
+	btrfs_set_stack_block_group_v2_remap_bytes(&bgi, block_group->remap_bytes);
+	btrfs_set_stack_block_group_v2_identity_remap_count(&bgi, block_group->identity_remap_count);
 	old_last_used = block_group->last_used;
 	block_group->last_used = block_group->used;
+	block_group->last_remap_bytes = block_group->remap_bytes;
+	block_group->last_identity_remap_count = block_group->identity_remap_count;
 	key.objectid = block_group->start;
 	key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
 	key.offset = block_group->length;
 	spin_unlock(&block_group->lock);
 
-	ret = btrfs_insert_item(trans, root, &key, &bgi, sizeof(bgi));
+	if (btrfs_fs_incompat(fs_info, REMAP_TREE))
+		size = sizeof(struct btrfs_block_group_item_v2);
+	else
+		size = sizeof(struct btrfs_block_group_item);
+
+	ret = btrfs_insert_item(trans, root, &key, &bgi, size);
 	if (ret < 0) {
 		spin_lock(&block_group->lock);
 		block_group->last_used = old_last_used;
@@ -3132,10 +3154,12 @@ static int update_block_group_item(struct btrfs_trans_handle *trans,
 	struct btrfs_root *root = btrfs_block_group_root(fs_info);
 	unsigned long bi;
 	struct extent_buffer *leaf;
-	struct btrfs_block_group_item bgi;
+	struct btrfs_block_group_item_v2 bgi;
 	struct btrfs_key key;
-	u64 old_last_used;
-	u64 used;
+	u64 old_last_used, old_last_remap_bytes;
+	u32 old_last_identity_remap_count;
+	u64 used, remap_bytes;
+	u32 identity_remap_count;
 
 	/*
 	 * Block group items update can be triggered out of commit transaction
@@ -3145,13 +3169,21 @@ static int update_block_group_item(struct btrfs_trans_handle *trans,
 	 */
 	spin_lock(&cache->lock);
 	old_last_used = cache->last_used;
+	old_last_remap_bytes = cache->last_remap_bytes;
+	old_last_identity_remap_count = cache->last_identity_remap_count;
 	used = cache->used;
-	/* No change in used bytes, can safely skip it. */
-	if (cache->last_used == used) {
+	remap_bytes = cache->remap_bytes;
+	identity_remap_count = cache->identity_remap_count;
+	/* No change in values, can safely skip it. */
+	if (cache->last_used == used &&
+	    cache->last_remap_bytes == remap_bytes &&
+	    cache->last_identity_remap_count == identity_remap_count) {
 		spin_unlock(&cache->lock);
 		return 0;
 	}
 	cache->last_used = used;
+	cache->last_remap_bytes = remap_bytes;
+	cache->last_identity_remap_count = identity_remap_count;
 	spin_unlock(&cache->lock);
 
 	key.objectid = cache->start;
@@ -3167,11 +3199,21 @@ static int update_block_group_item(struct btrfs_trans_handle *trans,
 
 	leaf = path->nodes[0];
 	bi = btrfs_item_ptr_offset(leaf, path->slots[0]);
-	btrfs_set_stack_block_group_used(&bgi, used);
-	btrfs_set_stack_block_group_chunk_objectid(&bgi,
-						   cache->global_root_id);
-	btrfs_set_stack_block_group_flags(&bgi, cache->flags);
-	write_extent_buffer(leaf, &bgi, bi, sizeof(bgi));
+	btrfs_set_stack_block_group_v2_used(&bgi, used);
+	btrfs_set_stack_block_group_v2_chunk_objectid(&bgi, cache->global_root_id);
+	btrfs_set_stack_block_group_v2_flags(&bgi, cache->flags);
+
+	if (btrfs_fs_incompat(fs_info, REMAP_TREE)) {
+		btrfs_set_stack_block_group_v2_remap_bytes(&bgi, cache->remap_bytes);
+		btrfs_set_stack_block_group_v2_identity_remap_count(&bgi,
+						cache->identity_remap_count);
+		write_extent_buffer(leaf, &bgi, bi,
+				    sizeof(struct btrfs_block_group_item_v2));
+	} else {
+		write_extent_buffer(leaf, &bgi, bi,
+				    sizeof(struct btrfs_block_group_item));
+	}
+
 fail:
 	btrfs_release_path(path);
 	/*
@@ -3186,6 +3228,8 @@ static int update_block_group_item(struct btrfs_trans_handle *trans,
 	if (ret < 0 && ret != -ENOENT) {
 		spin_lock(&cache->lock);
 		cache->last_used = old_last_used;
+		cache->last_remap_bytes = old_last_remap_bytes;
+		cache->last_identity_remap_count = old_last_identity_remap_count;
 		spin_unlock(&cache->lock);
 	}
 	return ret;
diff --git a/fs/btrfs/block-group.h b/fs/btrfs/block-group.h
index b0fb85a36d97..ecabb1a9fc0e 100644
--- a/fs/btrfs/block-group.h
+++ b/fs/btrfs/block-group.h
@@ -129,6 +129,8 @@ struct btrfs_block_group {
 	u64 flags;
 	u64 cache_generation;
 	u64 global_root_id;
+	u64 remap_bytes;
+	u32 identity_remap_count;
 
 	/*
 	 * The last committed used bytes of this block group, if the above @used
@@ -136,6 +138,11 @@ struct btrfs_block_group {
 	 * group item of this block group.
 	 */
 	u64 last_used;
+	/* The last committed remap_bytes value of this block group. */
+	u64 last_remap_bytes;
+	/* The last commited identity_remap_count value of this block group. */
+	u32 last_identity_remap_count;
+
 	/*
 	 * If the free space extent count exceeds this number, convert the block
 	 * group to bitmaps.
@@ -282,7 +289,8 @@ static inline bool btrfs_is_block_group_used(const struct btrfs_block_group *bg)
 {
 	lockdep_assert_held(&bg->lock);
 
-	return (bg->used > 0 || bg->reserved > 0 || bg->pinned > 0);
+	return (bg->used > 0 || bg->reserved > 0 || bg->pinned > 0 ||
+		bg->remap_bytes > 0);
 }
 
 static inline bool btrfs_is_block_group_data_only(const struct btrfs_block_group *block_group)
diff --git a/fs/btrfs/discard.c b/fs/btrfs/discard.c
index 89fe85778115..ee5f5b2788e1 100644
--- a/fs/btrfs/discard.c
+++ b/fs/btrfs/discard.c
@@ -373,7 +373,7 @@ 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)
+	if (block_group->used == 0 && block_group->remap_bytes == 0)
 		add_to_discard_unused_list(discard_ctl, block_group);
 	else
 		add_to_discard_list(discard_ctl, block_group);
diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c
index ead2e1e2a0bb..452394b34d01 100644
--- a/fs/btrfs/tree-checker.c
+++ b/fs/btrfs/tree-checker.c
@@ -688,6 +688,7 @@ static int check_block_group_item(struct extent_buffer *leaf,
 	u64 chunk_objectid;
 	u64 flags;
 	u64 type;
+	size_t exp_size;
 
 	/*
 	 * Here we don't really care about alignment since extent allocator can
@@ -699,10 +700,15 @@ static int check_block_group_item(struct extent_buffer *leaf,
 		return -EUCLEAN;
 	}
 
-	if (unlikely(item_size != sizeof(bgi))) {
+	if (btrfs_fs_incompat(fs_info, REMAP_TREE))
+		exp_size = sizeof(struct btrfs_block_group_item_v2);
+	else
+		exp_size = sizeof(struct btrfs_block_group_item);
+
+	if (unlikely(item_size != exp_size)) {
 		block_group_err(leaf, slot,
 			"invalid item size, have %u expect %zu",
-				item_size, sizeof(bgi));
+				item_size, exp_size);
 		return -EUCLEAN;
 	}
 
diff --git a/include/uapi/linux/btrfs_tree.h b/include/uapi/linux/btrfs_tree.h
index 76578426671c..86820a9644e8 100644
--- a/include/uapi/linux/btrfs_tree.h
+++ b/include/uapi/linux/btrfs_tree.h
@@ -1229,6 +1229,14 @@ struct btrfs_block_group_item {
 	__le64 flags;
 } __attribute__ ((__packed__));
 
+struct btrfs_block_group_item_v2 {
+	__le64 used;
+	__le64 chunk_objectid;
+	__le64 flags;
+	__le64 remap_bytes;
+	__le32 identity_remap_count;
+} __attribute__ ((__packed__));
+
 struct btrfs_free_space_info {
 	__le32 extent_count;
 	__le32 flags;