btrfs: Streamline btrfs_delalloc_reserve_metadata initial operations

The behavior of btrfs_delalloc_reserve_metadata depends on whether
the inode we are allocating for is the freespace inode or not. As it
stands if we are the free node we set 'flush' and 'delalloc_lock'
variable to certain values. Subsequently we check the values of those
vars and act accordingly. Instead, simplify things by having 1 if
which checks whether we are the freespace inode or not and do any
specific operation in either branches of that if. This makes the code
a bit easier to understand, as an added bonus it also shrinks the
compiled size:

add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-17 (-17)
Function                                     old     new   delta
btrfs_delalloc_reserve_metadata             1876    1859     -17
Total: Before=85966, After=85949, chg -0.02%

No functional changes.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Edmund Nadolski <enadolski@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent-tree.c

@@ -6061,13 +6061,13 @@ int btrfs_delalloc_reserve_metadata(struct btrfs_inode *inode, u64 num_bytes)
 	if (btrfs_is_free_space_inode(inode)) {
 		flush = BTRFS_RESERVE_NO_FLUSH;
 		delalloc_lock = false;
-	} else if (current->journal_info) {
-		flush = BTRFS_RESERVE_FLUSH_LIMIT;
-	}
+	} else {
+		if (current->journal_info)
+			flush = BTRFS_RESERVE_FLUSH_LIMIT;
 
-	if (flush != BTRFS_RESERVE_NO_FLUSH &&
-	    btrfs_transaction_in_commit(fs_info))
-		schedule_timeout(1);
+		if (btrfs_transaction_in_commit(fs_info))
+			schedule_timeout(1);
+	}
 
 	if (delalloc_lock)
 		mutex_lock(&inode->delalloc_mutex);