GFS2: Sort the ordered write list

This patch sorts the ordered write list for GFS2 writes.
This increases the throughput for simultaneous writes.
For example, if you have ten processes, all doing:
dd if=/dev/zero of=/mnt/gfs2/fileX
on different files, the throughput will be much better.
Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/log.c

@@ -19,6 +19,7 @@
 #include <linux/freezer.h>
 #include <linux/bio.h>
 #include <linux/writeback.h>
+#include <linux/list_sort.h>
 
 #include "gfs2.h"
 #include "incore.h"
@@ -566,6 +567,20 @@ static void log_flush_commit(struct gfs2_sbd *sdp)
 	log_write_header(sdp, 0, 0);
 }
 
+int bd_cmp(void *priv, struct list_head *a, struct list_head *b)
+{
+	struct gfs2_bufdata *bda, *bdb;
+
+	bda = list_entry(a, struct gfs2_bufdata, bd_le.le_list);
+	bdb = list_entry(b, struct gfs2_bufdata, bd_le.le_list);
+
+	if (bda->bd_bh->b_blocknr < bdb->bd_bh->b_blocknr)
+		return -1;
+	if (bda->bd_bh->b_blocknr > bdb->bd_bh->b_blocknr)
+		return 1;
+	return 0;
+}
+
 static void gfs2_ordered_write(struct gfs2_sbd *sdp)
 {
 	struct gfs2_bufdata *bd;
@@ -573,6 +588,7 @@ static void gfs2_ordered_write(struct gfs2_sbd *sdp)
 	LIST_HEAD(written);
 
 	gfs2_log_lock(sdp);
+	list_sort(NULL, &sdp->sd_log_le_ordered, &bd_cmp);
 	while (!list_empty(&sdp->sd_log_le_ordered)) {
 		bd = list_entry(sdp->sd_log_le_ordered.next, struct gfs2_bufdata, bd_le.le_list);
 		list_move(&bd->bd_le.le_list, &written);