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

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Date:	Mon, 6 Sep 2010 01:17:02 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Christoph Hellwig <hch@....de>, Tejun Heo <tj@...nel.org>,
	Jens Axboe <jaxboe@...ionio.com>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Nigel Cunningham <nigel@...onice.net>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 3/4] swap: do not send discards as barriers

From: Christoph Hellwig <hch@...radead.org>

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@....de>
Tested-by: Nigel Cunningham <nigel@...onice.net>
Signed-off-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Hugh Dickins <hughd@...gle.com>
Cc: Jens Axboe <jaxboe@...ionio.com>
Cc: James Bottomley <James.Bottomley@...senpartnership.com>
Cc: "Martin K. Petersen" <martin.petersen@...cle.com>
Cc: stable@...nel.org
---

 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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