diff --git a/ctree.h b/ctree.h
index 6d805ecd..5324f7b9 100644
--- a/ctree.h
+++ b/ctree.h
@@ -1062,15 +1062,32 @@ struct btrfs_space_info {
 	struct list_head list;
 };
 
+/* Block group allocation types */
+enum btrfs_alloc_type {
+
+	/* Regular first fit allocation */
+	BTRFS_ALLOC_FIT		= 0,
+
+	/*
+	 * Sequential allocation: this is for HMZONED mode and
+	 * will result in ignoring free space before a block
+	 * group allocation offset.
+	 */
+	BTRFS_ALLOC_SEQ		= 1,
+};
+
 struct btrfs_block_group_cache {
 	struct cache_extent cache;
 	struct btrfs_key key;
 	struct btrfs_block_group_item item;
 	struct btrfs_space_info *space_info;
 	struct btrfs_free_space_ctl *free_space_ctl;
+	enum btrfs_alloc_type alloc_type;
 	u64 bytes_super;
 	u64 pinned;
 	u64 flags;
+	u64 alloc_offset;
+	u64 write_offset;
 	int cached;
 	int ro;
 };
diff --git a/extent-tree.c b/extent-tree.c
index 5d49af5a..01660864 100644
--- a/extent-tree.c
+++ b/extent-tree.c
@@ -256,6 +256,14 @@ again:
 	if (cache->ro || !block_group_bits(cache, data))
 		goto new_group;
 
+	if (cache->alloc_type == BTRFS_ALLOC_SEQ) {
+		if (cache->key.offset - cache->alloc_offset < num)
+			goto new_group;
+		*start_ret = cache->key.objectid + cache->alloc_offset;
+		cache->alloc_offset += num;
+		return 0;
+	}
+
 	while(1) {
 		ret = find_first_extent_bit(&root->fs_info->free_space_cache,
 					    last, &start, &end, EXTENT_DIRTY);
@@ -282,6 +290,7 @@ out:
 			(unsigned long long)search_start);
 		return -ENOENT;
 	}
+	printf("nospace\n");
 	return -ENOSPC;
 
 new_group:
@@ -3143,6 +3152,176 @@ error:
 	return ret;
 }
 
+#ifdef BTRFS_ZONED
+static int
+btrfs_get_block_group_alloc_offset(struct btrfs_fs_info *fs_info,
+				   struct btrfs_block_group_cache *cache)
+{
+	struct btrfs_device *device;
+	struct btrfs_mapping_tree *map_tree = &fs_info->mapping_tree;
+	struct cache_extent *ce;
+	struct map_lookup *map;
+	u64 logical = cache->key.objectid;
+	u64 length = cache->key.offset;
+	u64 physical = 0;
+	int ret = 0;
+	int i;
+	u64 zone_size = fs_info->fs_devices->zone_size;
+	u64 *alloc_offsets = NULL;
+
+	if (!btrfs_fs_incompat(fs_info, HMZONED))
+		return 0;
+
+	/* Sanity check */
+	if (!IS_ALIGNED(length, zone_size)) {
+		fprintf(stderr, "unaligned block group at %llu", logical);
+		return -EIO;
+	}
+
+	/* Get the chunk mapping */
+	ce = search_cache_extent(&map_tree->cache_tree, logical);
+	if (!ce) {
+		fprintf(stderr, "failed to find block group at %llu", logical);
+		return -ENOENT;
+	}
+	map = container_of(ce, struct map_lookup, ce);
+
+	/*
+	 * Get the zone type: if the group is mapped to a non-sequential zone,
+	 * there is no need for the allocation offset (fit allocation is OK).
+	 */
+	device = map->stripes[0].dev;
+	physical = map->stripes[0].physical;
+	if (!zone_is_random_write(&device->zinfo, physical))
+		cache->alloc_type = BTRFS_ALLOC_SEQ;
+
+	/* check block group mapping */
+	alloc_offsets = calloc(map->num_stripes, sizeof(*alloc_offsets));
+	for (i = 0; i < map->num_stripes; i++) {
+		int is_sequential;
+		struct blk_zone zone;
+
+		device = map->stripes[i].dev;
+		physical = map->stripes[i].physical;
+
+		is_sequential = !zone_is_random_write(&device->zinfo, physical);
+		if ((is_sequential && cache->alloc_type != BTRFS_ALLOC_SEQ) ||
+		    (!is_sequential && cache->alloc_type == BTRFS_ALLOC_SEQ)) {
+			fprintf(stderr,
+				"found block group of mixed zone types");
+			ret = -EIO;
+			goto out;
+		}
+
+		if (!is_sequential)
+			continue;
+
+		WARN_ON(!IS_ALIGNED(physical, zone_size));
+		zone = device->zinfo.zones[physical / zone_size];
+
+		/*
+		 * The group is mapped to a sequential zone. Get the zone write
+		 * pointer to determine the allocation offset within the zone.
+		 */
+		switch (zone.cond) {
+		case BLK_ZONE_COND_OFFLINE:
+		case BLK_ZONE_COND_READONLY:
+			fprintf(stderr, "Offline/readonly zone %llu",
+				physical / fs_info->fs_devices->zone_size);
+			ret = -EIO;
+			goto out;
+		case BLK_ZONE_COND_EMPTY:
+			alloc_offsets[i] = 0;
+			break;
+		case BLK_ZONE_COND_FULL:
+			alloc_offsets[i] = zone_size;
+			break;
+		default:
+			/* Partially used zone */
+			alloc_offsets[i] = ((zone.wp - zone.start) << 9);
+			break;
+		}
+	}
+
+	if (cache->alloc_type != BTRFS_ALLOC_SEQ)
+		goto out;
+
+	switch (map->type & BTRFS_BLOCK_GROUP_PROFILE_MASK) {
+	case 0: /* single */
+	case BTRFS_BLOCK_GROUP_DUP:
+	case BTRFS_BLOCK_GROUP_RAID1:
+		for (i = 1; i < map->num_stripes; i++) {
+			if (alloc_offsets[i] != alloc_offsets[0]) {
+				fprintf(stderr,
+					"zones' write pointers mismatch\n");
+				ret = -EIO;
+				goto out;
+			}
+		}
+		cache->alloc_offset = alloc_offsets[0];
+		break;
+	case BTRFS_BLOCK_GROUP_RAID0:
+		cache->alloc_offset = alloc_offsets[0];
+		for (i = 1; i < map->num_stripes; i++) {
+			cache->alloc_offset += alloc_offsets[i];
+			if (alloc_offsets[0] < alloc_offsets[i]) {
+				fprintf(stderr,
+					"zones' write pointers mismatch\n");
+				ret = -EIO;
+				goto out;
+			}
+		}
+		break;
+	case BTRFS_BLOCK_GROUP_RAID10:
+		cache->alloc_offset = 0;
+		for (i = 0; i < map->num_stripes / map->sub_stripes; i++) {
+			int j;
+			int base;
+
+			base = i*map->sub_stripes;
+			for (j = 1; j < map->sub_stripes; j++) {
+				if (alloc_offsets[base] !=
+					alloc_offsets[base+j]) {
+					fprintf(stderr,
+						"zones' write pointer mismatch\n");
+					ret = -EIO;
+					goto out;
+				}
+			}
+
+			if (alloc_offsets[0] < alloc_offsets[base]) {
+				fprintf(stderr,
+					"zones' write pointer mismatch\n");
+				ret = -EIO;
+				goto out;
+			}
+			cache->alloc_offset += alloc_offsets[base];
+		}
+		break;
+	case BTRFS_BLOCK_GROUP_RAID5:
+	case BTRFS_BLOCK_GROUP_RAID6:
+		/* RAID5/6 is not supported yet */
+	default:
+		fprintf(stderr, "Unsupported profile %llu\n",
+			map->type & BTRFS_BLOCK_GROUP_PROFILE_MASK);
+		ret = -EINVAL;
+		goto out;
+	}
+
+out:
+	cache->write_offset = cache->alloc_offset;
+	free(alloc_offsets);
+	return ret;
+}
+#else
+static int
+btrfs_get_block_group_alloc_offset(struct btrfs_fs_info *fs_info,
+				   struct btrfs_block_group_cache *cache)
+{
+	return 0;
+}
+#endif
+
 int btrfs_read_block_groups(struct btrfs_root *root)
 {
 	struct btrfs_path *path;
@@ -3226,6 +3405,10 @@ int btrfs_read_block_groups(struct btrfs_root *root)
 		BUG_ON(ret);
 		cache->space_info = space_info;
 
+		ret = btrfs_get_block_group_alloc_offset(info, cache);
+		if (ret)
+			goto error;
+
 		/* use EXTENT_LOCKED to prevent merging */
 		set_extent_bits(block_group_cache, found_key.objectid,
 				found_key.objectid + found_key.offset - 1,
@@ -3255,6 +3438,9 @@ btrfs_add_block_group(struct btrfs_fs_info *fs_info, u64 bytes_used, u64 type,
 	cache->key.objectid = chunk_offset;
 	cache->key.offset = size;
 
+	ret = btrfs_get_block_group_alloc_offset(fs_info, cache);
+	BUG_ON(ret);
+
 	cache->key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
 	btrfs_set_block_group_used(&cache->item, bytes_used);
 	btrfs_set_block_group_chunk_objectid(&cache->item,
diff --git a/transaction.c b/transaction.c
index ecafbb15..0e49b8b7 100644
--- a/transaction.c
+++ b/transaction.c
@@ -115,16 +115,32 @@ int __commit_transaction(struct btrfs_trans_handle *trans,
 {
 	u64 start;
 	u64 end;
+	u64 next = 0;
 	struct btrfs_fs_info *fs_info = root->fs_info;
 	struct extent_buffer *eb;
 	struct extent_io_tree *tree = &fs_info->extent_cache;
+	struct btrfs_block_group_cache *bg = NULL;
 	int ret;
 
 	while(1) {
+again:
 		ret = find_first_extent_bit(tree, 0, &start, &end,
 					    EXTENT_DIRTY);
 		if (ret)
 			break;
+		bg = btrfs_lookup_first_block_group(fs_info, start);
+		BUG_ON(!bg);
+		if (bg->alloc_type == BTRFS_ALLOC_SEQ &&
+		    bg->key.objectid + bg->write_offset < start) {
+			next = bg->key.objectid + bg->write_offset;
+			BUG_ON(next + fs_info->nodesize > start);
+			eb = btrfs_find_create_tree_block(fs_info, next);
+			btrfs_mark_buffer_dirty(eb);
+			free_extent_buffer(eb);
+			goto again;
+		}
+		if (bg->alloc_type == BTRFS_ALLOC_SEQ)
+			bg->write_offset += (end + 1 - start);
 		while(start <= end) {
 			eb = find_first_extent_buffer(tree, start);
 			BUG_ON(!eb || eb->start != start);
