The swap code already uses synchronous discards, no need to add I/O barriers.

Signed-off-by: Christoph Hellwig <hch@lst.de>

Index: linux-2.6/mm/swapfile.c
===================================================================
--- linux-2.6.orig/mm/swapfile.c	2010-08-17 16:49:28.312010428 +0200
+++ linux-2.6/mm/swapfile.c	2010-08-17 16:49:43.694255853 +0200
@@ -140,7 +140,7 @@ static int discard_swap(struct swap_info
 	if (nr_blocks) {
 		err = blkdev_issue_discard(si->bdev, start_block,
 				nr_blocks, GFP_KERNEL,
-				BLKDEV_IFL_WAIT | BLKDEV_IFL_BARRIER);
+				BLKDEV_IFL_WAIT);
 		if (err)
 			return err;
 		cond_resched();
@@ -152,7 +152,7 @@ static int discard_swap(struct swap_info
 
 		err = blkdev_issue_discard(si->bdev, start_block,
 				nr_blocks, GFP_KERNEL,
-				BLKDEV_IFL_WAIT | BLKDEV_IFL_BARRIER);
+				BLKDEV_IFL_WAIT);
 		if (err)
 			break;
 
@@ -191,8 +191,7 @@ static void discard_swap_cluster(struct
 			start_block <<= PAGE_SHIFT - 9;
 			nr_blocks <<= PAGE_SHIFT - 9;
 			if (blkdev_issue_discard(si->bdev, start_block,
-				    nr_blocks, GFP_NOIO, BLKDEV_IFL_WAIT |
-							BLKDEV_IFL_BARRIER))
+				    nr_blocks, GFP_NOIO, BLKDEV_IFL_WAIT))
 				break;
 		}