[PATCH] xfs: optimize log flushing in xfs_fsync

[Christoph Hellwig]

If we have a pinned inode it must have a log item attached to it.
Usually that log item will have ili_last_lsn already set, in which
case we only need to flush the log up to that LSN instead of doing
a full log force.  This gives speedups of about 5% in some fsync
heavy workloads.

Signed-off-by: Christoph Hellwig <hch at lst.de>

Index: xfs/fs/xfs/xfs_vnodeops.c
===================================================================
--- xfs.orig/fs/xfs/xfs_vnodeops.c	2010-02-04 17:38:33.679254119 +0100
+++ xfs/fs/xfs/xfs_vnodeops.c	2010-02-04 17:38:51.606006156 +0100
@@ -626,8 +626,14 @@ xfs_fsync(
 		 * force the log.
 		 */
 		if (xfs_ipincount(ip)) {
-			error = _xfs_log_force(ip->i_mount, XFS_LOG_SYNC,
-					       &log_flushed);
+			if (ip->i_itemp->ili_last_lsn) {
+				error = _xfs_log_force_lsn(ip->i_mount,
+						ip->i_itemp->ili_last_lsn,
+						XFS_LOG_SYNC, &log_flushed);
+			} else {
+				error = _xfs_log_force(ip->i_mount,
+						XFS_LOG_SYNC, &log_flushed);
+			}
 		}
 	} else	{
 		/*