[PATCH 3/4] swap: do not send discards as barriers

[Hugh Dickins]

From: Christoph Hellwig <hch@xxxxxxxxxxxxx>

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

This fixes the worst of the terrible slowdown in swap allocation for
hibernation, reported on 2.6.35 by Nigel Cunningham; but does not
entirely eliminate that regression.

tj: superflous newlines removed.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Tested-by: Nigel Cunningham <nigel@xxxxxxxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jens Axboe <jaxboe@xxxxxxxxxxxx>
Cc: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
Cc: "Martin K. Petersen" <martin.petersen@xxxxxxxxxx>
Cc: stable@xxxxxxxxxx
---

 mm/swapfile.c |    9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

--- swap2/mm/swapfile.c	2010-09-05 22:45:54.000000000 -0700
+++ swap3/mm/swapfile.c	2010-09-05 22:47:21.000000000 -0700
@@ -139,8 +139,7 @@ static int discard_swap(struct swap_info
 	nr_blocks = ((sector_t)se->nr_pages - 1) << (PAGE_SHIFT - 9);
 	if (nr_blocks) {
 		err = blkdev_issue_discard(si->bdev, start_block,
-				nr_blocks, GFP_KERNEL,
-				BLKDEV_IFL_WAIT | BLKDEV_IFL_BARRIER);
+				nr_blocks, GFP_KERNEL, BLKDEV_IFL_WAIT);
 		if (err)
 			return err;
 		cond_resched();
@@ -151,8 +150,7 @@ static int discard_swap(struct swap_info
 		nr_blocks = (sector_t)se->nr_pages << (PAGE_SHIFT - 9);
 
 		err = blkdev_issue_discard(si->bdev, start_block,
-				nr_blocks, GFP_KERNEL,
-				BLKDEV_IFL_WAIT | BLKDEV_IFL_BARRIER);
+				nr_blocks, GFP_KERNEL, BLKDEV_IFL_WAIT);
 		if (err)
 			break;
 
@@ -191,8 +189,7 @@ 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;
 		}
 
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