Description of problem:
There is a large performance hit when using the -o sync mount option on gfs
filesystems.  The problem is that pages are not being flushed to disk when the
gfs_writepage routine is accessed due to the transaction not yet being
completed.  The pages are currently only getting flushed when pdflush is executed.

Version-Release number of selected component (if applicable):


How reproducible:
Mount the gfs filesystem with the -o sync option.
Do a cp of a 1 GB file to the mounted filesystem.  This will take on the order
of hours to complete.


Steps to Reproduce:
1. mount -t gfs -o sync /dev/mapper/VolCluster0 /mnt/gfs0
2. dd if=/dev/zero of=/tmp/bigfile bs=1024k count=1000
3. time cp /tmp/bigfile /mnt/gfs0
  
Actual results:
Command takes 6+ hours to complete.

Expected results:
Command should take a few minutes depending on process and I/O system.

Additional info:  Propose Patch
RCS file: /cvs/cluster/cluster/gfs-kernel/src/gfs/ops_file.c,v
retrieving revision 1.18
diff -u -r1.18 ops_file.c
--- gfs-kernel/src/gfs/ops_file.c       4 Mar 2005 00:59:13 -0000       1.18
+++ gfs-kernel/src/gfs/ops_file.c       14 Nov 2005 17:07:45 -0000
@@ -815,8 +815,14 @@

        gfs_trans_end(sdp);

-       if (file->f_flags & O_SYNC)
+       if (file->f_flags & O_SYNC || IS_SYNC(inode)) {
                gfs_log_flush_glock(ip->i_gl);
+               error = filemap_fdatawrite(ip->i_gl);
+               if (error == 0)
+                       error = filemap_fdatawait(file->f_mapping);
+               if (error)
+                       goto fail_ipres;
+       }

        if (alloc_required) {
                gfs_assert_warn(sdp, count != size ||