ext4: optimize orphan_list handling for ext4_setattr

Surprisingly chown() on ext4 is not SMP scalable operation. 
Due to unconditional orphan_del(NULL, inode) in ext4_setattr()
result in significant performance overhead because of global orphan
mutex, especially in no-journal mode (where orphan_add() is noop).
It is possible to skip explicit orphan_del if possible.
Results of fchown() micro-benchmark in no-journal mode
while (1) {
   iteration++;
   fchown(fd, uid, gid);
   fchown(fd, uid + 1, gid + 1)
}
measured: iterations per millisecond
| nr_tasks | w/o patch | with patch |
|        1 |       142 |        185 |
|        4 |       109 |        642 |

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 7 insertions, 3 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 9e60d0b8fa75..3ba237b0b2aa 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5281,6 +5281,7 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
 {
         struct inode *inode = dentry->d_inode;
         int error, rc = 0;
+        int orphan = 0;
         const unsigned int ia_valid = attr->ia_valid;
 
         error = inode_change_ok(inode, attr);
@@ -5336,8 +5337,10 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
                         error = PTR_ERR(handle);
                         goto err_out;
                 }
-
-                error = ext4_orphan_add(handle, inode);
+                if (ext4_handle_valid(handle)) {
+                        error = ext4_orphan_add(handle, inode);
+                        orphan = 1;
+                }
                 EXT4_I(inode)->i_disksize = attr->ia_size;
                 rc = ext4_mark_inode_dirty(handle, inode);
                 if (!error)
@@ -5355,6 +5358,7 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
                                         goto err_out;
                                 }
                                 ext4_orphan_del(handle, inode);
+                                orphan = 0;
                                 ext4_journal_stop(handle);
                                 goto err_out;
                         }
@@ -5377,7 +5381,7 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
          * If the call to ext4_truncate failed to get a transaction handle at
          * all, we need to clean up the in-core orphan list manually.
          */
-        if (inode->i_nlink)
+        if (orphan && inode->i_nlink)
                 ext4_orphan_del(NULL, inode);
 
         if (!rc && (ia_valid & ATTR_MODE))