Btrfs: only adjust outstanding_extents when we do a short write

We have this weird dance where we always inc outstanding_extents when we do a
O_DIRECT write, even if we allocate the entire range.  To get around this we
also drop the metadata space if we successfully write.  This is an unnecessary
dance, we only need to jack up outstanding_extents if we don't satisfy the
entire range request in get_blocks_direct, otherwise we are good using our
original reservation.  So drop the unconditional inc and the drop of the
metadata space that we have for the unconditional inc.  Thanks,
Signed-off-by: NJosef Bacik <jbacik@fb.com>
Reviewed-by: NLiu Bo <bo.li.liu@oracle.com>
Signed-off-by: NChris Mason <clm@fb.com>

fs/btrfs/inode.c

@@ -7155,6 +7155,7 @@ static int btrfs_get_blocks_direct(struct inode *inode, sector_t iblock,
 	u64 start = iblock << inode->i_blkbits;
 	u64 lockstart, lockend;
 	u64 len = bh_result->b_size;
+	u64 orig_len = len;
 	int unlock_bits = EXTENT_LOCKED;
 	int ret = 0;
 
@@ -7290,9 +7291,11 @@ static int btrfs_get_blocks_direct(struct inode *inode, sector_t iblock,
 		if (start + len > i_size_read(inode))
 			i_size_write(inode, start + len);
 
-		spin_lock(&BTRFS_I(inode)->lock);
-		BTRFS_I(inode)->outstanding_extents++;
-		spin_unlock(&BTRFS_I(inode)->lock);
+		if (len < orig_len) {
+			spin_lock(&BTRFS_I(inode)->lock);
+			BTRFS_I(inode)->outstanding_extents++;
+			spin_unlock(&BTRFS_I(inode)->lock);
+		}
 
 		ret = set_extent_bit(&BTRFS_I(inode)->io_tree, lockstart,
 				     lockstart + len - 1, EXTENT_DELALLOC, NULL,
@@ -8073,8 +8076,6 @@ static ssize_t btrfs_direct_IO(int rw, struct kiocb *iocb,
 		else if (ret >= 0 && (size_t)ret < count)
 			btrfs_delalloc_release_space(inode,
 						     count - (size_t)ret);
-		else
-			btrfs_delalloc_release_metadata(inode, 0);
 	}
 out:
 	if (wakeup)