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[Cluster-devel] [GFS2 PATCH] Reduce truncate IO traffic



Current GFS2 setattr call unconditionally invokes do_shrink even the requested size and actual file size are equal. This has generated large amount of extra IOs found during NFS benchmark runs. This patch moves the relevant logic out of shrink code path. Since setattr is a system call, the time stamps update is still required.

-- Wendy


Current GFS2 setattr call unconditionally invokes do_shrink even the 
requested size and actual file size are equal. This has generated large 
amount of extra IOs found during NFS benchmark runs. This patch moves 
the relevant logic out of shrink code path. Since setattr is a system 
call, time stamps update is still required.

 Signed-off-by: S. Wendy Cheng <wcheng redhat com>

 bmap.c |   32 +++++++++++++++++++++++++++++++-
 1 files changed, 31 insertions(+), 1 deletion(-)

--- gfs2-2.6-nmw/fs/gfs2/bmap.c	2007-08-11 19:06:12.000000000 -0400
+++ linux/fs/gfs2/bmap.c	2007-08-20 00:24:58.000000000 -0400
@@ -1085,6 +1085,33 @@ static int do_shrink(struct gfs2_inode *
 	return error;
 }
 
+static int do_touch(struct gfs2_inode *ip, u64 size)
+{
+	struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
+	struct buffer_head *dibh;
+	int error;
+
+	error = gfs2_trans_begin(sdp, RES_DINODE, 0);
+	if (error)
+		return error;
+
+	down_write(&ip->i_rw_mutex);
+
+	error = gfs2_meta_inode_buffer(ip, &dibh);
+	if (error)
+		goto do_touch_out;
+
+	ip->i_inode.i_mtime = ip->i_inode.i_ctime = CURRENT_TIME;
+	gfs2_trans_add_bh(ip->i_gl, dibh, 1);
+	gfs2_dinode_out(ip, dibh->b_data);
+	brelse(dibh);
+
+do_touch_out:
+	up_write(&ip->i_rw_mutex);
+	gfs2_trans_end(sdp);
+	return error;
+}
+
 /**
  * gfs2_truncatei - make a file a given size
  * @ip: the inode
@@ -1105,8 +1132,11 @@ int gfs2_truncatei(struct gfs2_inode *ip
 
 	if (size > ip->i_di.di_size)
 		error = do_grow(ip, size);
-	else
+	else if (size < ip->i_di.di_size)
 		error = do_shrink(ip, size);
+	else
+		/* update time stamps */
+		error = do_touch(ip, size);
 
 	return error;
 }

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