swap: do not send discards as barriers

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@kernel.org: superflous newlines removed]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Nigel Cunningham <nigel@tuxonice.net>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Jens Axboe <jaxboe@fusionio.com>
Cc: James Bottomley <James.Bottomley@hansenpartnership.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 6 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index ed5151079f59..1894dead0b58 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -139,8 +139,7 @@ static int discard_swap(struct swap_info_struct *si)
         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_struct *si)
                 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 swap_info_struct *si,
                         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;
                 }