diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index f53470112670b2de73343e635e4304fd08816468..e90d7c597ef3a651a15458b8b3108a02065c6d3e 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -961,7 +961,6 @@ static noinline int cow_file_range(struct inode *inode,
 	u64 alloc_hint = 0;
 	u64 num_bytes;
 	unsigned long ram_size;
-	u64 disk_num_bytes;
 	u64 cur_alloc_size = 0;
 	u64 blocksize = fs_info->sectorsize;
 	struct btrfs_key ins;
@@ -979,7 +978,6 @@ static noinline int cow_file_range(struct inode *inode,
 
 	num_bytes = ALIGN(end - start + 1, blocksize);
 	num_bytes = max(blocksize,  num_bytes);
-	disk_num_bytes = num_bytes;
 
 	inode_should_defrag(BTRFS_I(inode), start, end, num_bytes, SZ_64K);
 
@@ -1010,15 +1008,14 @@ static noinline int cow_file_range(struct inode *inode,
 		}
 	}
 
-	BUG_ON(disk_num_bytes >
-	       btrfs_super_total_bytes(fs_info->super_copy));
+	BUG_ON(num_bytes > btrfs_super_total_bytes(fs_info->super_copy));
 
 	alloc_hint = get_extent_allocation_hint(inode, start, num_bytes);
 	btrfs_drop_extent_cache(BTRFS_I(inode), start,
 			start + num_bytes - 1, 0);
 
-	while (disk_num_bytes > 0) {
-		cur_alloc_size = disk_num_bytes;
+	while (num_bytes > 0) {
+		cur_alloc_size = num_bytes;
 		ret = btrfs_reserve_extent(root, cur_alloc_size, cur_alloc_size,
 					   fs_info->sectorsize, 0, alloc_hint,
 					   &ins, 1, 1);
@@ -1082,11 +1079,10 @@ static noinline int cow_file_range(struct inode *inode,
 					     delalloc_end, locked_page,
 					     EXTENT_LOCKED | EXTENT_DELALLOC,
 					     page_ops);
-		if (disk_num_bytes < cur_alloc_size)
-			disk_num_bytes = 0;
+		if (num_bytes < cur_alloc_size)
+			num_bytes = 0;
 		else
-			disk_num_bytes -= cur_alloc_size;
-		num_bytes -= cur_alloc_size;
+			num_bytes -= cur_alloc_size;
 		alloc_hint = ins.objectid + ins.offset;
 		start += cur_alloc_size;
 		extent_reserved = false;