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[PATCH] xfs: optimize fsync on directories

To: xfs@xxxxxxxxxxx
Subject: [PATCH] xfs: optimize fsync on directories
From: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Date: Sun, 2 Oct 2011 10:25:16 -0400
User-agent: Mutt/1.5.21 (2010-09-15)
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-transaction updates, an 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 make a difference when doing lots of fsync that do not actually
have to commit the inode, e.g. becase an ealier fsync already pushed
the log far enough.

The new xfs_dir_fsync is identifical 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>

Index: xfs/fs/xfs/xfs_file.c
===================================================================
--- xfs.orig/fs/xfs/xfs_file.c  2011-09-26 10:56:48.607884402 +0200
+++ xfs/fs/xfs/xfs_file.c       2011-09-26 10:59:56.922867311 +0200
@@ -124,6 +124,35 @@ 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,
+       loff_t                  start,
+       loff_t                  end,
+       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,
@@ -1140,7 +1169,7 @@ const struct file_operations xfs_dir_fil
 #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 = {
Index: xfs/fs/xfs/xfs_trace.h
===================================================================
--- xfs.orig/fs/xfs/xfs_trace.h 2011-09-26 11:00:05.367867252 +0200
+++ xfs/fs/xfs/xfs_trace.h      2011-09-26 11:00:22.090368120 +0200
@@ -576,6 +576,7 @@ 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);

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