From: Hisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp>
Date: Thu, 17 Apr 2008 14:38:59 +0000 (-0400)
Subject: ext4: fdatasync should skip metadata writeout when overwriting
X-Git-Tag: v2.6.26-rc1~345^2~44
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=53c550e9750434ddc4275fe0405170e0d1b46731;p=linux-2.6

ext4: fdatasync should skip metadata writeout when overwriting

Currently fdatasync is identical to fsync in ext3.

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 on ext3 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>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
---

diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
index 8d50879d1c..a04a1ac4e0 100644
--- a/fs/ext4/fsync.c
+++ b/fs/ext4/fsync.c
@@ -72,6 +72,9 @@ int ext4_sync_file(struct file * file, struct dentry *dentry, int datasync)
 		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.