On Wed, 18 Aug 2010, Christoph Hellwig wrote:
> The swap code already uses synchronous discards, no need to add I/O barriers.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
(though if you happened to respin, I'd be be glad for those newlines
between GFP_KERNEL, BLKDEV_IFL_WAIT to go away now)
This patch could go in any time now: I may want to push it in and
get it to 35-stable, because it certainly helps against the swap
discard regression that Nigel reported (though I've not yet seen
his numbers with this). However, I don't think it eliminates the
regression, so I've more testing and experimenting to do before
deciding about it - the right answer may just be to disable swap
discard, as you asked for long ago.
Hugh
>
> 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;
> }
>
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