GFS2: Sort buffer lists by inplace block number

This patch simply sort the data and metadata buffer lists by their
inplace block number.  This makes gfs2_log_flush issue the inplace IO
in sequential order, which will hopefully speed up writing the IO
out to disk.
Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/lops.c

@@ -16,6 +16,7 @@
 #include <linux/gfs2_ondisk.h>
 #include <linux/bio.h>
 #include <linux/fs.h>
+#include <linux/list_sort.h>
 
 #include "gfs2.h"
 #include "incore.h"
@@ -401,6 +402,20 @@ static void gfs2_check_magic(struct buffer_head *bh)
 	kunmap_atomic(kaddr);
 }
 
+static int blocknr_cmp(void *priv, struct list_head *a, struct list_head *b)
+{
+	struct gfs2_bufdata *bda, *bdb;
+
+	bda = list_entry(a, struct gfs2_bufdata, bd_list);
+	bdb = list_entry(b, struct gfs2_bufdata, bd_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_before_commit(struct gfs2_sbd *sdp, unsigned int limit,
 				unsigned int total, struct list_head *blist,
 				bool is_databuf)
@@ -413,6 +428,7 @@ static void gfs2_before_commit(struct gfs2_sbd *sdp, unsigned int limit,
 	__be64 *ptr;
 
 	gfs2_log_lock(sdp);
+	list_sort(NULL, blist, blocknr_cmp);
 	bd1 = bd2 = list_prepare_entry(bd1, blist, bd_list);
 	while(total) {
 		num = total;