em->mod_start = em->start;
        em->mod_len = em->len;
 
-       if (test_bit(EXTENT_FLAG_PREALLOC, &em->flags)) {
+       if (test_bit(EXTENT_FLAG_FILLING, &em->flags)) {
                prealloc = true;
-               clear_bit(EXTENT_FLAG_PREALLOC, &em->flags);
+               clear_bit(EXTENT_FLAG_FILLING, &em->flags);
        }
 
        try_merge_map(tree, em);
 
 #define EXTENT_FLAG_VACANCY 2 /* no file extent item found */
 #define EXTENT_FLAG_PREALLOC 3 /* pre-allocated extent */
 #define EXTENT_FLAG_LOGGING 4 /* Logging this extent */
+#define EXTENT_FLAG_FILLING 5 /* Filling in a preallocated extent */
 
 struct extent_map {
        struct rb_node rb_node;
 
                        em->orig_block_len = disk_num_bytes;
                        em->bdev = root->fs_info->fs_devices->latest_bdev;
                        set_bit(EXTENT_FLAG_PINNED, &em->flags);
-                       set_bit(EXTENT_FLAG_PREALLOC, &em->flags);
+                       set_bit(EXTENT_FLAG_FILLING, &em->flags);
                        while (1) {
                                write_lock(&em_tree->lock);
                                ret = add_extent_mapping(em_tree, em);
        em->orig_block_len = orig_block_len;
        set_bit(EXTENT_FLAG_PINNED, &em->flags);
        if (type == BTRFS_ORDERED_PREALLOC)
-               set_bit(EXTENT_FLAG_PREALLOC, &em->flags);
+               set_bit(EXTENT_FLAG_FILLING, &em->flags);
 
        do {
                btrfs_drop_extent_cache(inode, em->start,