fs: pull inode->i_lock up out of writeback_single_inode

First thing we do in writeback_single_inode() is take the i_lock and
the last thing we do is drop it. A caller already holds the i_lock,
so pull the i_lock out of writeback_single_inode() to reduce the
round trips on this lock during inode writeback.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 11 insertions, 7 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index ed800656356b..b5ed541fb137 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -332,9 +332,9 @@ static void inode_wait_for_writeback(struct inode *inode)
 }
 
 /*
- * Write out an inode's dirty pages.  Called under inode_wb_list_lock.  Either
- * the caller has an active reference on the inode or the inode has I_WILL_FREE
- * set.
+ * Write out an inode's dirty pages.  Called under inode_wb_list_lock and
+ * inode->i_lock.  Either the caller has an active reference on the inode or
+ * the inode has I_WILL_FREE set.
  *
  * If `wait' is set, wait on the writeout.
  *
@@ -349,7 +349,9 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
         unsigned dirty;
         int ret;
 
-        spin_lock(&inode->i_lock);
+        assert_spin_locked(&inode_wb_list_lock);
+        assert_spin_locked(&inode->i_lock);
+
         if (!atomic_read(&inode->i_count))
                 WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
         else
@@ -365,7 +367,6 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
                  * completed a full scan of b_io.
                  */
                 if (wbc->sync_mode != WB_SYNC_ALL) {
-                        spin_unlock(&inode->i_lock);
                         requeue_io(inode);
                         return 0;
                 }
@@ -456,7 +457,6 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
                 }
         }
         inode_sync_complete(inode);
-        spin_unlock(&inode->i_lock);
         return ret;
 }
 
@@ -544,7 +544,6 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
                 }
 
                 __iget(inode);
-                spin_unlock(&inode->i_lock);
 
                 pages_skipped = wbc->pages_skipped;
                 writeback_single_inode(inode, wbc);
@@ -555,6 +554,7 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
                          */
                         redirty_tail(inode);
                 }
+                spin_unlock(&inode->i_lock);
                 spin_unlock(&inode_wb_list_lock);
                 iput(inode);
                 cond_resched();
@@ -1309,7 +1309,9 @@ int write_inode_now(struct inode *inode, int sync)
 
         might_sleep();
         spin_lock(&inode_wb_list_lock);
+        spin_lock(&inode->i_lock);
         ret = writeback_single_inode(inode, &wbc);
+        spin_unlock(&inode->i_lock);
         spin_unlock(&inode_wb_list_lock);
         if (sync)
                 inode_sync_wait(inode);
@@ -1333,7 +1335,9 @@ int sync_inode(struct inode *inode, struct writeback_control *wbc)
         int ret;
 
         spin_lock(&inode_wb_list_lock);
+        spin_lock(&inode->i_lock);
         ret = writeback_single_inode(inode, wbc);
+        spin_unlock(&inode->i_lock);
         spin_unlock(&inode_wb_list_lock);
         return ret;
 }