[PATCH] ext3,4:fdatasync should skip metadata writeout

[PATCH] ext3,4:fdatasync should skip metadata writeout

[Hisashi Hifumi]

[-- Attachment #1: Type: text/plain, Size: 1255 bytes --]

Hi.
Currently fdatasync is identical to fsync in ext3,4.
I think fdatasync should skip journal flush in data=ordered and data=writeback mode
because this syscall is not required to synchronize the metadata.

My patch as below is similar to the approach of GFS2's fsync code(gfs2_fsync).

Thanks.

Signed-off-by :Hisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp>

diff -Nrup linux-2.6.24-rc2.org/fs/ext3/fsync.c linux-2.6.24-rc2/fs/ext3/fsync.c
--- linux-2.6.24-rc2.org/fs/ext3/fsync.c	2007-11-07 06:57:46.000000000 +0900
+++ linux-2.6.24-rc2/fs/ext3/fsync.c	2007-11-15 17:50:24.000000000 +0900
@@ -72,6 +72,9 @@ int ext3_sync_file(struct file * file, s
 		goto out;
 	}
 
+	if (datasync)
+		goto out;	
+
 	/*
 	* The VFS has written the file data.  If the inode is unaltered
 	* then we need not start a commit.
diff -Nrup linux-2.6.24-rc2.org/fs/ext4/fsync.c linux-2.6.24-rc2/fs/ext4/fsync.c
--- linux-2.6.24-rc2.org/fs/ext4/fsync.c	2007-11-07 06:57:46.000000000 +0900
+++ linux-2.6.24-rc2/fs/ext4/fsync.c	2007-11-15 17:50:54.000000000 +0900
@@ -72,6 +72,9 @@ int ext4_sync_file(struct file * file, s
 		goto out;
 	}
 
+	if (datasync)
+		goto out;
+
 	/*
 	* The VFS has written the file data.  If the inode is unaltered
 	* then we need not start a commit.

[-- Attachment #2: patch-2624rc2-ext34-fdatasync.txt --]
[-- Type: application/octet-stream, Size: 927 bytes --]

diff -Nrup linux-2.6.24-rc2.org/fs/ext3/fsync.c linux-2.6.24-rc2/fs/ext3/fsync.c
--- linux-2.6.24-rc2.org/fs/ext3/fsync.c	2007-11-07 06:57:46.000000000 +0900
+++ linux-2.6.24-rc2/fs/ext3/fsync.c	2007-11-15 17:50:24.000000000 +0900
@@ -72,6 +72,9 @@ int ext3_sync_file(struct file * file, s
 		goto out;
 	}
 
+	if (datasync)
+		goto out;	
+
 	/*
 	 * The VFS has written the file data.  If the inode is unaltered
 	 * then we need not start a commit.
diff -Nrup linux-2.6.24-rc2.org/fs/ext4/fsync.c linux-2.6.24-rc2/fs/ext4/fsync.c
--- linux-2.6.24-rc2.org/fs/ext4/fsync.c	2007-11-07 06:57:46.000000000 +0900
+++ linux-2.6.24-rc2/fs/ext4/fsync.c	2007-11-15 17:50:54.000000000 +0900
@@ -72,6 +72,9 @@ int ext4_sync_file(struct file * file, s
 		goto out;
 	}
 
+	if (datasync)
+		goto out;
+
 	/*
 	 * The VFS has written the file data.  If the inode is unaltered
 	 * then we need not start a commit.

Re: [PATCH] ext3,4:fdatasync should skip metadata writeout

[Andrew Morton]

On Fri, 16 Nov 2007 11:47:27 +0900 Hisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp> wrote:

> Currently fdatasync is identical to fsync in ext3,4.
> I think fdatasync should skip journal flush in data=ordered and data=writeback mode
> because this syscall is not required to synchronize the metadata.

I suppose so.  Although one wonders what earthly point there is in syncing
a file's data if we haven't yet written out the metadata which is required
for locating that data.

IOW, fdatasync() is only useful if the application knows that it is overwriting
already-instantiated blocks.

In which case it might as well have used fsync().  For ext2-style filesystems,
anyway.

hm.  It needs some thought.

Re: [PATCH] ext3,4:fdatasync should skip metadata writeout

[Jörn Engel]

On Thu, 15 November 2007 18:59:19 -0800, Andrew Morton wrote:
> On Fri, 16 Nov 2007 11:47:27 +0900 Hisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp> wrote:
> 
> > Currently fdatasync is identical to fsync in ext3,4.
> > I think fdatasync should skip journal flush in data=ordered and data=writeback mode
> > because this syscall is not required to synchronize the metadata.
> 
> I suppose so.  Although one wonders what earthly point there is in syncing
> a file's data if we haven't yet written out the metadata which is required
> for locating that data.
> 
> IOW, fdatasync() is only useful if the application knows that it is overwriting
> already-instantiated blocks.
> 
> In which case it might as well have used fsync().  For ext2-style filesystems,
> anyway.

fsync() will sync an inode even if only i_atime was changed.
fdatasync() would ignore such changes.  I guess atime was the major
reason for creating fdatasync() in the first place.

The patch I sent you just minutes ago sorta documents this.
I_DIRTY_DATASYNC was added with patch-2.4.0-test12 for just this reason.

So basically an application can almost always use fdatasync() instead of
fsync() and rely on the kernel to only cut corners, if doing so will not
endanger the data synced to disk.

Jörn

-- 
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http://www.gzip.org/zlib/feldspar.html
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Re: [PATCH] ext3,4:fdatasync should skip metadata writeout

[Bryan Henderson]

>fsync() will sync an inode even if only i_atime was changed.
>fdatasync() would ignore such changes.  I guess atime was the major
>reason for creating fdatasync() in the first place.

I think it was mtime.  One doesn't normally call any kind of sync when one 
is just reading the file.  But keeping an accurate mtime is often not 
worth the I/O.

And theoretically, there could be all kinds of "truly meta" metadata that 
changes as you write to the file but would probably be considered more 
expendable than the file's actual data.

But I think it was always intended that fdatasync() would sync the data in 
a meaningful way -- i.e. such that the data can be retrieved after a 
system failure; it surely wasn't meant for the user to understand 
filesystem internals.  I've heard the term "data-related metadata" to 
distinguish such things as allocation maps and pointer blocks from mtime, 
permissions, etc.

--
Bryan Henderson                     IBM Almaden Research Center
San Jose CA                         Filesystems

Re: [PATCH] ext3,4:fdatasync should skip metadata writeout

[Wendy Cheng]

Andrew Morton wrote:

>On Fri, 16 Nov 2007 11:47:27 +0900 Hisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp> wrote:
>
>  
>
>>Currently fdatasync is identical to fsync in ext3,4.
>>I think fdatasync should skip journal flush in data=ordered and data=writeback mode
>>because this syscall is not required to synchronize the metadata.
>>    
>>
>
>I suppose so.  Although one wonders what earthly point there is in syncing
>a file's data if we haven't yet written out the metadata which is required
>for locating that data.
>
>IOW, fdatasync() is only useful if the application knows that it is overwriting
>already-instantiated blocks.
>
>In which case it might as well have used fsync().  For ext2-style filesystems,
>anyway.
>
>hm.  It needs some thought.
>
>  
>

There are non-trivial amount of performance critical programs, 
particularly in financial application segment ported from legacy UNIX 
platforms, know the difference between fsync() and fdatasync(). Those 
can certainly take advantages of this separation. Don't underestimate 
the talents of these application programmers.

-- Wendy

Re: [PATCH] ext3,4:fdatasync should skip metadata writeout

[Andrew Morton]

On Thu, 15 Nov 2007 22:47:40 -0500 Wendy Cheng <wcheng@redhat.com> wrote:

> Andrew Morton wrote:
> 
> >On Fri, 16 Nov 2007 11:47:27 +0900 Hisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp> wrote:
> >
> >  
> >
> >>Currently fdatasync is identical to fsync in ext3,4.
> >>I think fdatasync should skip journal flush in data=ordered and data=writeback mode
> >>because this syscall is not required to synchronize the metadata.
> >>    
> >>
> >
> >I suppose so.  Although one wonders what earthly point there is in syncing
> >a file's data if we haven't yet written out the metadata which is required
> >for locating that data.
> >
> >IOW, fdatasync() is only useful if the application knows that it is overwriting
> >already-instantiated blocks.
> >
> >In which case it might as well have used fsync().  For ext2-style filesystems,
> >anyway.
> >
> >hm.  It needs some thought.
> >
> >  
> >
> 
> There are non-trivial amount of performance critical programs, 
> particularly in financial application segment ported from legacy UNIX 
> platforms, know the difference between fsync() and fdatasync(). Those 
> can certainly take advantages of this separation. Don't underestimate 
> the talents of these application programmers.
> 

If they're that good, they'll be using sync_file_range() ;)

Re: [PATCH] ext3,4:fdatasync should skip metadata writeout

[Hisashi Hifumi]

At 11:59 07/11/16, Andrew Morton wrote:
 >
 >I suppose so.  Although one wonders what earthly point there is in syncing
 >a file's data if we haven't yet written out the metadata which is required
 >for locating that data.
 >
 >IOW, fdatasync() is only useful if the application knows that it is overwriting
 >already-instantiated blocks.
 >
 >In which case it might as well have used fsync().  For ext2-style filesystems,
 >anyway.
 >
 >hm.  It needs some thought.

I did a test to measure the file overwriting performance difference between
original fdatasync and one that skips journal flush.
The test program and obtained result is as follows:

Test program source code:

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <time.h>

#define BUFSIZE 8192
#define LOOP 1024*1024

main(void)
{
	int i;
	int fd;
	char buf[BUFSIZE];
	time_t t1,t2;

	memset(buf,0,BUFSIZE);

	fd = open("testfile", O_CREAT|O_RDWR);
	if (fd < 0)
		perror("cannot open file\n");

	for (i = 0; i < LOOP; i++)
		write(fd,buf,BUFSIZE);
	fsync(fd);

	lseek(fd, 0, SEEK_SET);
	time(&t1);
	for (i = 0; i < LOOP; i++) {
		write(fd,buf,BUFSIZE);
		fdatasync(fd);
	}
	time(&t2);

	printf("%d sec\n",t2-t1);
}

Result:

  2.6.24-rc3:

	264 sec

  2.6.23-rc3-fdatasync-skips-journal-flush-patched

	253 sec

Hardware environment:
  Dell Poweredge 850
  CPU Pentium D  3GHz
  memory 4GB
  HDD Maxtor 6L160M0


I got somewhat better result from the patched ext3 skipping journal flush.

Some DBMS such as PostgreSQL can use fdatasync. So I think skipping
journal flush on overwriting leads to performance improvement for
these application.

I am for the notion that skipping metadata writeout unconditionally is wrong,
and "important metadata" such as i_size, block-bitmap etc should be
synched even if fdatasync is issued , but unimportant meta such as
mtime and ctime update can be ignored when a file is overwritten.

[RESEND] [PATCH] ext3,4:fdatasync should skip metadata writeout when overwriting

[Hisashi Hifumi]

Hi.

Currently fdatasync is identical to fsync in ext3,4.
I think fdatasync should skip journal flush in data=ordered and data=writeback mode
when it overwrites to already-instantiated blocks on HDD.
When I_DIRTY_DATASYNC flag is not set, fdatasync should skip journal writeout
because this indicates only atime or/and mtime updates.  

Following patch is the same approach of ext2's fsync code(ext2_sync_file).

I did a performance test using the sysbench.

#sysbench --num-threads=128 --max-requests=50000 --test=fileio --file-total-size=128G 
--file-test-mode=rndwr --file-fsync-mode=fdatasync run

The result was:

	-2.6.24
	Operations performed:  0 Read, 50080 Write, 59600 Other = 109680 Total
	Read 0b  Written 782.5Mb  Total transferred 782.5Mb  (12.116Mb/sec)
	  775.45 Requests/sec executed

	Test execution summary:
	    total time:                          64.5814s
	    total number of events:              50080
	    total time taken by event execution: 3713.9836
	    per-request statistics:
	         min:                            0.0000s
	         avg:                            0.0742s
	         max:                            0.9375s
	         approx.  95 percentile:         0.2901s

	Threads fairness:
	    events (avg/stddev):           391.2500/23.26
	    execution time (avg/stddev):   29.0155/1.99


	-2.6.24-patched
	Operations performed:  0 Read, 50009 Write, 61596 Other = 111605 Total
	Read 0b  Written 781.39Mb  Total transferred 781.39Mb  (16.419Mb/sec)
	 1050.83 Requests/sec executed

	Test execution summary:
	    total time:                          47.5900s
	    total number of events:              50009
	    total time taken by event execution: 2934.5768
	    per-request statistics:
 	         min:                            0.0000s
	         avg:                            0.0587s
 	         max:                            0.8938s
	         approx.  95 percentile:         0.1993s

	Threads fairness:
	    events (avg/stddev):           390.6953/22.64
	    execution time (avg/stddev):   22.9264/1.17


Filesystem I/O throughput was improved.

Thanks.

Signed-off-by :Hisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp>

diff -Nrup linux-2.6.24.org/fs/ext3/fsync.c linux-2.6.24/fs/ext3/fsync.c
--- linux-2.6.24.org/fs/ext3/fsync.c	2008-01-25 07:58:37.000000000 +0900
+++ linux-2.6.24/fs/ext3/fsync.c	2008-02-04 12:42:42.000000000 +0900
@@ -72,6 +72,9 @@ int ext3_sync_file(struct file * file, s
 		goto out;
 	}
 
+	if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
+		goto out;
+
 	/*
 	 * The VFS has written the file data.  If the inode is unaltered
 	 * then we need not start a commit.
diff -Nrup linux-2.6.24.org/fs/ext4/fsync.c linux-2.6.24/fs/ext4/fsync.c
--- linux-2.6.24.org/fs/ext4/fsync.c	2008-01-25 07:58:37.000000000 +0900
+++ linux-2.6.24/fs/ext4/fsync.c	2008-02-04 12:43:37.000000000 +0900
@@ -72,6 +72,9 @@ int ext4_sync_file(struct file * file, s
 		goto out;
 	}
 
+        if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
+                goto out;
+
 	/*
 	 * The VFS has written the file data.  If the inode is unaltered
 	 * then we need not start a commit.

Re: [RESEND] [PATCH] ext3,4:fdatasync should skip metadata writeout when overwriting

[Jan Kara]

  Hi,

> Currently fdatasync is identical to fsync in ext3,4.
> I think fdatasync should skip journal flush in data=ordered and data=writeback mode
> when it overwrites to already-instantiated blocks on HDD.
> When I_DIRTY_DATASYNC flag is not set, fdatasync should skip journal writeout
> because this indicates only atime or/and mtime updates.  
> 
> Following patch is the same approach of ext2's fsync code(ext2_sync_file).
> 
> I did a performance test using the sysbench.
> 
> #sysbench --num-threads=128 --max-requests=50000 --test=fileio --file-total-size=128G 
> --file-test-mode=rndwr --file-fsync-mode=fdatasync run
> 
> The result was:
> 
> 	-2.6.24
> 	Operations performed:  0 Read, 50080 Write, 59600 Other = 109680 Total
> 	Read 0b  Written 782.5Mb  Total transferred 782.5Mb  (12.116Mb/sec)
> 	  775.45 Requests/sec executed
> 
> 	Test execution summary:
> 	    total time:                          64.5814s
> 	    total number of events:              50080
> 	    total time taken by event execution: 3713.9836
> 	    per-request statistics:
> 	         min:                            0.0000s
> 	         avg:                            0.0742s
> 	         max:                            0.9375s
> 	         approx.  95 percentile:         0.2901s
> 
> 	Threads fairness:
> 	    events (avg/stddev):           391.2500/23.26
> 	    execution time (avg/stddev):   29.0155/1.99
> 
> 
> 	-2.6.24-patched
> 	Operations performed:  0 Read, 50009 Write, 61596 Other = 111605 Total
> 	Read 0b  Written 781.39Mb  Total transferred 781.39Mb  (16.419Mb/sec)
> 	 1050.83 Requests/sec executed
> 
> 	Test execution summary:
> 	    total time:                          47.5900s
> 	    total number of events:              50009
> 	    total time taken by event execution: 2934.5768
> 	    per-request statistics:
>  	         min:                            0.0000s
> 	         avg:                            0.0587s
>  	         max:                            0.8938s
> 	         approx.  95 percentile:         0.1993s
> 
> 	Threads fairness:
> 	    events (avg/stddev):           390.6953/22.64
> 	    execution time (avg/stddev):   22.9264/1.17
> 
> 
> Filesystem I/O throughput was improved.
> 
> Thanks.
> 
> Signed-off-by :Hisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp>
  Yes, the patch looks fine. You can add
Acked-by: Jan Kara <jack@suse.cz>
  if you wish.
								Honza

> diff -Nrup linux-2.6.24.org/fs/ext3/fsync.c linux-2.6.24/fs/ext3/fsync.c
> --- linux-2.6.24.org/fs/ext3/fsync.c	2008-01-25 07:58:37.000000000 +0900
> +++ linux-2.6.24/fs/ext3/fsync.c	2008-02-04 12:42:42.000000000 +0900
> @@ -72,6 +72,9 @@ int ext3_sync_file(struct file * file, s
>  		goto out;
>  	}
>  
> +	if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
> +		goto out;
> +
>  	/*
>  	 * The VFS has written the file data.  If the inode is unaltered
>  	 * then we need not start a commit.
> diff -Nrup linux-2.6.24.org/fs/ext4/fsync.c linux-2.6.24/fs/ext4/fsync.c
> --- linux-2.6.24.org/fs/ext4/fsync.c	2008-01-25 07:58:37.000000000 +0900
> +++ linux-2.6.24/fs/ext4/fsync.c	2008-02-04 12:43:37.000000000 +0900
> @@ -72,6 +72,9 @@ int ext4_sync_file(struct file * file, s
>  		goto out;
>  	}
>  
> +        if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
> +                goto out;
> +
>  	/*
>  	 * The VFS has written the file data.  If the inode is unaltered
>  	 * then we need not start a commit.
> 
> -
> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
-- 
Jan Kara <jack@suse.cz>
SuSE CR Labs

Re: [RESEND] [PATCH] ext3,4:fdatasync should skip metadata writeout when overwriting

[Hisashi Hifumi]

>> Signed-off-by :Hisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp>
>  Yes, the patch looks fine. You can add
>Acked-by: Jan Kara <jack@suse.cz>
>  if you wish.
>								Honza

Thank you for your comment.
Please merge my patch.

Thanks.

[PATCH] ext3,4:fdatasync should skip metadata writeout when overwriting

Currently fdatasync is identical to fsync in ext3,4.
I think fdatasync should skip journal flush in data=ordered and data=writeback mode
when it overwrites to already-instantiated blocks on HDD.
When I_DIRTY_DATASYNC flag is not set, fdatasync should skip journal writeout
because this indicates only atime or/and mtime updates.  

Following patch is the same approach of ext2's fsync code(ext2_sync_file).

I did a performance test using the sysbench.

#sysbench --num-threads=128 --max-requests=50000 --test=fileio --file-total-size=128G 
--file-test-mode=rndwr --file-fsync-mode=fdatasync run

The result was:

	-2.6.24
	Operations performed:  0 Read, 50080 Write, 59600 Other = 109680 Total
	Read 0b  Written 782.5Mb  Total transferred 782.5Mb  (12.116Mb/sec)
	  775.45 Requests/sec executed

	Test execution summary:
	    total time:                          64.5814s
	    total number of events:              50080
	    total time taken by event execution: 3713.9836
	    per-request statistics:
	         min:                            0.0000s
	         avg:                            0.0742s
	         max:                            0.9375s
	         approx.  95 percentile:         0.2901s

	Threads fairness:
	    events (avg/stddev):           391.2500/23.26
	    execution time (avg/stddev):   29.0155/1.99


	-2.6.24-patched
	Operations performed:  0 Read, 50009 Write, 61596 Other = 111605 Total
	Read 0b  Written 781.39Mb  Total transferred 781.39Mb  (16.419Mb/sec)
	1050.83 Requests/sec executed

	Test execution summary:
	    total time:                          47.5900s
	    total number of events:              50009
	    total time taken by event execution: 2934.5768
	    per-request statistics:
 	         min:                            0.0000s
	         avg:                            0.0587s
 	         max:                            0.8938s
	         approx.  95 percentile:         0.1993s

	Threads fairness:
	    events (avg/stddev):           390.6953/22.64
	    execution time (avg/stddev):   22.9264/1.17


Filesystem I/O throughput was improved.

Signed-off-by :Hisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp>
Acked-by: Jan Kara <jack@suse.cz>

diff -Nrup linux-2.6.24.org/fs/ext3/fsync.c linux-2.6.24/fs/ext3/fsync.c
--- linux-2.6.24.org/fs/ext3/fsync.c	2008-01-25 07:58:37.000000000 +0900
+++ linux-2.6.24/fs/ext3/fsync.c	2008-02-04 12:42:42.000000000 +0900
@@ -72,6 +72,9 @@ int ext3_sync_file(struct file * file, s
 		goto out;
 	}
 
+	if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
+		goto out;
+
 	/*
 	* The VFS has written the file data.  If the inode is unaltered
 	* then we need not start a commit.
diff -Nrup linux-2.6.24.org/fs/ext4/fsync.c linux-2.6.24/fs/ext4/fsync.c
--- linux-2.6.24.org/fs/ext4/fsync.c	2008-01-25 07:58:37.000000000 +0900
+++ linux-2.6.24/fs/ext4/fsync.c	2008-02-04 12:43:37.000000000 +0900
@@ -72,6 +72,9 @@ int ext4_sync_file(struct file * file, s
 		goto out;
 	}
 
+        if (datasync && !(inode->i_state & I_DIRTY_DATASYNC))
+                goto out;
+
 	/*
 	* The VFS has written the file data.  If the inode is unaltered
 	* then we need not start a commit.

Re: [PATCH] ext3,4:fdatasync should skip metadata writeout

[Jörn Engel]

On Fri, 16 November 2007 11:47:27 +0900, Hisashi Hifumi wrote:
> 
> diff -Nrup linux-2.6.24-rc2.org/fs/ext3/fsync.c linux-2.6.24-rc2/fs/ext3/fsync.c
> --- linux-2.6.24-rc2.org/fs/ext3/fsync.c	2007-11-07 06:57:46.000000000 +0900
> +++ linux-2.6.24-rc2/fs/ext3/fsync.c	2007-11-15 17:50:24.000000000 +0900
> @@ -72,6 +72,9 @@ int ext3_sync_file(struct file * file, s
>  		goto out;
>  	}
>  
> +	if (datasync)
> +		goto out;	
> +
>  	/*
>  	* The VFS has written the file data.  If the inode is unaltered
>  	* then we need not start a commit.

This is wrong.  If I_DIRTY_DATASYNC is set, the inode needs to be
written even for datasync.

How about the patch below?

Jörn

-- 
Audacity augments courage; hesitation, fear.
-- Publilius Syrus


Signed-off-by: Jörn Engel <joern@logfs.org>
---

 fs/ext3/fsync.c |    3 ++-
 fs/ext4/fsync.c |    3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

--- git_I_DIRTY/fs/ext3/fsync.c~ext3_datasync	2007-11-15 20:51:54.000000000 +0100
+++ git_I_DIRTY/fs/ext3/fsync.c	2007-11-16 04:42:28.000000000 +0100
@@ -76,7 +76,8 @@ int ext3_sync_file(struct file * file, s
 	 * The VFS has written the file data.  If the inode is unaltered
 	 * then we need not start a commit.
 	 */
-	if (inode->i_state & (I_DIRTY_SYNC|I_DIRTY_DATASYNC)) {
+	if (((inode->i_state & I_DIRTY_SYNC) && !datasync)
+			|| (inode->i_state & I_DIRTY_DATASYNC)) {
 		struct writeback_control wbc = {
 			.sync_mode = WB_SYNC_ALL,
 			.nr_to_write = 0, /* sys_fsync did this */
--- git_I_DIRTY/fs/ext4/fsync.c~ext3_datasync	2007-11-15 20:51:54.000000000 +0100
+++ git_I_DIRTY/fs/ext4/fsync.c	2007-11-16 04:44:29.000000000 +0100
@@ -76,7 +76,8 @@ int ext4_sync_file(struct file * file, s
 	 * The VFS has written the file data.  If the inode is unaltered
 	 * then we need not start a commit.
 	 */
-	if (inode->i_state & (I_DIRTY_SYNC|I_DIRTY_DATASYNC)) {
+	if (((inode->i_state & I_DIRTY_SYNC) && !datasync)
+			|| (inode->i_state & I_DIRTY_DATASYNC)) {
 		struct writeback_control wbc = {
 			.sync_mode = WB_SYNC_ALL,
 			.nr_to_write = 0, /* sys_fsync did this */