[PATCH 014/102] xfs: optimize fsync on directories

[Dave Chinner <david@xxxxxxxxxxxxx>]

From: Christoph Hellwig <hch@xxxxxxxxxxxxx>

Upstream commit: 1da2f2dbf2d2aaa1b0f6ca2f61fcf07e24eb659b

Directories are only updated transactionally, which means fsync only
needs to flush the log the inode is currently dirty, but not bother
with checking for dirty data, non-transactional updates, and most
importanly doesn't have to flush disk caches except as part of a
transaction commit.

While the first two optimizations can't easily be measured, the
latter actually makes a difference when doing lots of fsync that do
not actually have to commit the inode, e.g. because an earlier fsync
already pushed the log far enough.

The new xfs_dir_fsync is identical to xfs_nfs_commit_metadata except
for the prototype, but I'm not sure creating a common helper for the
two is worth it given how simple the functions are.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Alex Elder <aelder@xxxxxxx>
---
 fs/xfs/linux-2.6/xfs_file.c  |   29 ++++++++++++++++++++++++++++-
 fs/xfs/linux-2.6/xfs_trace.h |    1 +
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/linux-2.6/xfs_file.c b/fs/xfs/linux-2.6/xfs_file.c
index 67d392a..185a337 100644
--- a/fs/xfs/linux-2.6/xfs_file.c
+++ b/fs/xfs/linux-2.6/xfs_file.c
@@ -124,6 +124,33 @@ xfs_iozero(
        return (-status);
 }
 
+/*
+ * Fsync operations on directories are much simpler than on regular files,
+ * as there is no file data to flush, and thus also no need for explicit
+ * cache flush operations, and there are no non-transaction metadata updates
+ * on directories either.
+ */
+STATIC int
+xfs_dir_fsync(
+       struct file             *file,
+       int                     datasync)
+{
+       struct xfs_inode        *ip = XFS_I(file->f_mapping->host);
+       struct xfs_mount        *mp = ip->i_mount;
+       xfs_lsn_t               lsn = 0;
+
+       trace_xfs_dir_fsync(ip);
+
+       xfs_ilock(ip, XFS_ILOCK_SHARED);
+       if (xfs_ipincount(ip))
+               lsn = ip->i_itemp->ili_last_lsn;
+       xfs_iunlock(ip, XFS_ILOCK_SHARED);
+
+       if (!lsn)
+               return 0;
+       return _xfs_log_force_lsn(mp, lsn, XFS_LOG_SYNC, NULL);
+}
+
 STATIC int
 xfs_file_fsync(
        struct file             *file,
@@ -1141,7 +1168,7 @@ const struct file_operations xfs_dir_file_operations = {
 #ifdef CONFIG_COMPAT
        .compat_ioctl   = xfs_file_compat_ioctl,
 #endif
-       .fsync          = xfs_file_fsync,
+       .fsync          = xfs_dir_fsync,
 };
 
 static const struct vm_operations_struct xfs_file_vm_ops = {
diff --git a/fs/xfs/linux-2.6/xfs_trace.h b/fs/xfs/linux-2.6/xfs_trace.h
index d48b7a5..fae13a0 100644
--- a/fs/xfs/linux-2.6/xfs_trace.h
+++ b/fs/xfs/linux-2.6/xfs_trace.h
@@ -577,6 +577,7 @@ DEFINE_INODE_EVENT(xfs_vm_bmap);
 DEFINE_INODE_EVENT(xfs_file_ioctl);
 DEFINE_INODE_EVENT(xfs_file_compat_ioctl);
 DEFINE_INODE_EVENT(xfs_ioctl_setattr);
+DEFINE_INODE_EVENT(xfs_dir_fsync);
 DEFINE_INODE_EVENT(xfs_file_fsync);
 DEFINE_INODE_EVENT(xfs_destroy_inode);
 DEFINE_INODE_EVENT(xfs_write_inode);
-- 
1.7.10